INVEST SUB-ADVISORY REGARDING MML EMERGING GROWTH
  
  EXHIBIT
   D(18)
  
 INVESTMENT
   SUB-ADVISORY AGREEMENT
  
         This Investment
   Sub-Advisory Agreement (this “Sub-Advisory Agreement”), is by and
   between RS Investment Management, L.P. (the “Sub-Adviser”) and
   Massachusetts Mutual Life Insurance Company, a mutual life insurance company
   organized under the laws of the Commonwealth of Massachusetts
   (“MassMutual”), for the MML Emerging Growth Fund (the
   “Fund”), a series of MML Series Investment Fund (the
   “Trust”), a Massachusetts business trust which is an open-end
   diversified management investment company registered as such with the
   Securities and Exchange Commission (the “Commission”) pursuant to
   the Investment Company Act of 1940, as amended (the “Act”),
   effective as of the 1st day of May, 2000.
  
         WHEREAS, the Trust
   has appointed MassMutual as the investment adviser for the Fund pursuant to
   the terms of an Investment Advisory Agreement (the “Advisory
   Agreement”);
  
         WHEREAS, the Advisory
   Agreement provides that MassMutual may, at its option, subject to approval
   by the Trustees of the Trust and, to the extent necessary, the shareholders
   of the Fund, appoint a sub-adviser to assume certain responsibilities and
   obligations of MassMutual under the Advisory Agreement;
  
         WHEREAS, MassMutual
   and the Sub-Adviser are investment advisers registered with the Commission
   as such under the Investment Advisers Act of 1940, as amended (the
   “Advisers Act”); and
  
         WHEREAS, MassMutual
   desires to appoint the Sub-Adviser as its sub-adviser for the Fund and the
   Sub-Adviser is willing to act in such capacity upon the terms herein set
   forth;
  
         NOW THEREFORE, in
   consideration of the premises and of the mutual covenants herein contained,
   MassMutual, the Fund and the Sub-Adviser, the parties hereto, intending to
   be legally bound, hereby agree as follows:
  
 1.  General Provision.
  
         (a) 
    MassMutual hereby employs the Sub-Adviser and the Sub-Adviser hereby
   undertakes to act as the investment sub-adviser of the Fund to provide
   investment advice and to perform for the Fund such other duties and
   functions as are hereinafter set forth. The Sub-Adviser shall, in all
   matters, give to the Fund and the Trust’s Board of Trustees, directly
   or through MassMutual, the benefit of the Sub-Adviser’s best judgment,
   effort, advice and recommendations and shall, at all times conform to, and
   use its best efforts to ensure the Fund conforms to:
  
 
  
   |  |         (i)  the
     provisions of the Act and any rules or regulations thereunder;
   
  
 
  
 
  
   |  |         (ii)  any
     other applicable provisions of state or federal law;
   
  
 
  
 
  
   |  |         (iii) 
      the provisions of the Agreement and Declaration of Trust and Bylaws
     of the Trust, as amended from time to time (collectively referred to as
     the “Trust Documents”);
   
  
 
  
 
  
   |  |         (iv) 
      policies and determinations of the Board of Trustees of the Trust
     and MassMutual;
   
  
 
  
 
  
   |  |         (v)  the
     fundamental and non-fundamental policies and investment restrictions of
     the Fund as reflected in the Trust’s registration statement under the
     Act or as such policies may, from time to time, be amended by the
     Fund’s shareholders; and
   
  
 
  
 
  
   |  |         (vi)  the
     Prospectus and Statement of Additional Information of the Fund in effect
     from time to time (collectively referred to as the “Disclosure
     Documents”).
   
  
 
  
         (b)  The
   appropriate officers and employees of the Sub-Adviser shall be available
   upon reasonable notice for consultation with any of the Trustees and
   officers of the Trust and MassMutual with respect to any matter dealing with
   the business and affairs of the Fund, such as the valuation of portfolio
   securities of the Fund, including but not limited to securities that are
   either not registered for public sale or securities not traded on any
   securities market.
  
 
   2.  Duties of the Sub-Adviser.
  
         (a)  The
   Sub-Adviser shall, subject to the direction and control by the Trust’s
   Board of Trustees or MassMutual, to the extent MassMutual’s direction
   is not inconsistent with that of the Board of Trustees, (i) regularly
   provide investment advice and recommendations to the Fund, directly or
   through MassMutual, with respect to the Fund’s investments, investment
   policies and the purchase, sale or other disposition of securities and other
   investments; (ii) supervise and monitor continuously the investment program
   of the Fund and the composition of its portfolio and determine what
   securities or other investments shall be purchased or sold by the Fund;
   (iii) arrange, subject to the provisions of Section 6 hereof, for the
   purchase of securities and other investments for the Fund and the sale of
   securities and other investments held in the portfolio of the Fund; (iv)
   provide reports on the foregoing to the Board of Trustees at each Board
   meeting; and (v) undertake to do anything incidental to the foregoing to
   facilitate the performance of the Sub-Adviser’s obligations hereunder,
   including voting or exercising any consent rights with respect to such
   securities or investments.
  
         (b)  The
   Sub-Adviser shall provide to MassMutual such reports for the Fund, and in
   such time frames, as MassMutual shall reasonably request or as required by
   applicable law or regulation.
  
         (c) 
    Provided that none of MassMutual, the Fund or the Trust shall be
   required to pay any compensation other than as provided by the terms of this
   Sub-Advisory Agreement and subject to the provisions of Section 5 hereof,
   the Sub-Adviser may obtain investment information, research or assistance
   from any other person, firm or corporation to supplement, update or
   otherwise improve its investment management services.
  
         (d) 
    Provided that nothing herein shall be deemed to protect the
   Sub-Adviser from liability for willful misfeasance, bad faith or gross
   negligence in the performance of its duties, or reckless disregard to its
   obligations and duties under this Sub-Advisory Agreement, the Sub-Adviser
   shall not be liable for any loss sustained by the Fund, MassMutual or any
   other person under or in respect of the services performed by the
   Sub-Adviser pursuant to this Sub-Advisory Agreement.
  
         (e)  The
   Sub-Adviser shall, upon request of MassMutual or the Fund, make all material
   disclosures to MassMutual and the Fund regarding itself and its partners,
   officers, directors, shareholders, employees, affiliates or any person who
   controls any of the foregoing, including, but not limited to, information
   regarding any change in control in the Sub-Adviser or any change in its key
   personnel, information regarding any material adverse change in the
   condition (financial or otherwise) of the Sub-Adviser or any person who
   controls the Sub-Adviser, information regarding the investment performance
   and general investment methods of the Sub-Adviser, its principals and
   affiliates, information that MassMutual reasonably deems material to the
   Fund or necessary to enable MassMutual to monitor the performance of the
   Sub-Adviser and information that is required, in the reasonable judgment of
   MassMutual, to be disclosed in any filings required by any governmental
   agency or by any applicable law, regulation, rule or order.
  
         (f)  The
   Sub-Adviser shall provide MassMutual with any information in the
   Sub-Adviser’s possession necessary for the compilation and maintenance
   of such records with respect to the Fund’s operations as may reasonably
   be required.
  
         (g)  The
   Sub-Adviser shall provide MassMutual, upon reasonable prior written request
   by MassMutual to the Sub-Adviser, with access to inspect at the
   Sub-Adviser’s office the books and records of the Sub-Adviser relating
   to the Fund and the Sub-Adviser’s performance hereunder and such other
   books and records of the Sub-Adviser as are reasonably necessary to confirm
   that the Sub-Adviser has complied with its obligations and duties under this
   Sub-Advisory Agreement.
  
 3.  Other Activities.
  
         (a) 
    Nothing in this Sub-Advisory Agreement shall prevent MassMutual or the
   Sub-Adviser or any officer thereof from acting as investment adviser or
   sub-adviser for any other person, firm, corporation or other entity and
   shall not in any way limit or restrict MassMutual or the Sub-Adviser or any
   of their respective directors,
 officers, members, stockholders, partners or employees from buying, selling,
   or trading any securities for its own account or for the account of others
   for whom it or they may be acting, provided that such activities are in
   compliance with U.S. federal and state securities laws, regulations and
   rules and will not adversely affect or otherwise impair the performance by
   any party of its duties and obligations under this Sub-Advisory
   Agreement.
  
         (b)  To the
   extent that a particular investment is suitable for both the Fund and the
   Sub-Adviser’s other clients, such investment will be allocated among
   the Fund and such other clients in a manner that is, in the reasonable
   judgment of the Sub-Adviser, fair and equitable in the circumstances.
   Subject to the foregoing, the Sub-Adviser agrees that it will not knowingly
   or deliberately favor any other account managed or controlled by it or any
   of its principals or affiliates over the Fund. The Sub-Adviser, upon
   reasonable request and receipt of adequate assurances of confidentiality,
   shall provide MassMutual with an explanation of the differences, if any, in
   performance between the Fund and any other account with investment
   objectives and policies similar to the Fund for which the Sub-Adviser, or
   any one of its principals or affiliates, acts as investment
   adviser.
  
 4.  Compensation of the Sub-Adviser.
  
         MassMutual agrees to
   pay the Sub-Adviser and the Sub-Adviser agrees to accept as full
   compensation for the performance of all functions and duties on its part to
   be performed pursuant to the provisions hereof, a fee paid quarterly, in
   arrears, at the following rate: an annual rate of .65% on the first $200
   million of Aggregate Assets; .60% on the next $200 million of Aggregate
   Assets; and, subject to MassMutual adding another Concert Investment Program
   investment option that is either sub-advised by the Sub-Adviser or that is a
   proprietary or retail mutual fund of the Sub-Adviser that MassMutual
   purchases through a separate investment account, .55% on Aggregate Assets in
   excess of $400 million. For the purposes of this Sub-Advisory Agreement,
   “Aggregate Assets” shall mean the aggregate of (i) the average
   daily net assets of the Fund determined at the close of the New York Stock
   Exchange on each day that the Exchange is open for trading, and (ii) the
   average daily net assets of all other funds or accounts of MassMutual or its
   affiliates, including other funds registered under the Act, for which the
   Sub-Adviser provides investment advisory services, and which have
   substantially the same investment objective and strategy, determined at the
   close of the Exchange on each day that the Exchange is open for trading.
   MassMutual shall pay the Sub-Adviser such fee not later than the tenth
   (10th) business day immediately following the end of each calendar quarter.
   Aggregate Assets for which the Sub-Adviser provides investment advisory
   services shall mean only equity securities and securities convertible into
   equity securities, but shall not include cash or cash equivalents (and do
   not include the Sub-Adviser’s proprietary mutual funds or insurance
   trusts which are purchased by the Fund or by MassMutual registered or
   unregistered separate investment accounts).
  
 5.  Portfolio Transactions and
   Brokerage.
  
         (a)  The
   Sub-Adviser is authorized, in arranging the purchase and sale of the
   Fund’s publicly-traded portfolio securities, to employ or deal with
   such members of securities exchanges, brokers or dealers (hereinafter
   “broker-dealers”), as may, in its best judgment, implement the
   policy of the Fund to obtain, at reasonable expense, the best execution of
   the Fund’s portfolio transactions.
  
         (b)  The
   Sub-Adviser may effect the purchase and sale of securities (which are
   otherwise publicly traded) in private transactions on such terms and
   conditions as are customary in such transactions, may use a broker to effect
   such transactions, and may enter into a contract in which the broker acts
   either as principal or as agent.
  
         (c)  The
   Sub-Adviser shall select broker-dealers to effect the Fund’s portfolio
   transactions on the basis of its estimate of their ability to obtain best
   execution of particular and related portfolio transactions. The abilities of
   a broker-dealer to obtain best execution of particular portfolio
   transaction(s) will be judged by the Sub-Adviser on the basis of all
   relevant factors and considerations including, insofar as feasible, the
   execution capabilities required by the transaction or transactions; the
   ability and willingness of the broker-dealer to facilitate the Fund’s
   portfolio transactions by participating therein for its own account; the
   importance to the Fund of speed, efficiency or confidentiality; the
   broker-dealer’s apparent familiarity with sources from or to whom
   particular securities might be purchased or sold; other matters involved in
   the receipt of brokerage and research services in
 accordance with Section 28(e) of the Securities Exchange Act of 1934, as
   amended; as well as any other matters relevant to the selection of a
   broker-dealer for particular and related transactions of the Fund; and such
   other considerations as the Board of Trustees of the Trust or MassMutual
   determine and provide to the Sub-Adviser from time to time. Subject to the
   foregoing, the Sub-Adviser may also consider sales of shares of the Fund, or
   may consider or follow the recommendations of MassMutual that take such
   sales into account, as factors in the selection of broker-dealers to effect
   the Fund’s portfolio transactions. Notwithstanding the above, nothing
   herein shall require the Sub-Adviser to use a broker-dealer which provides
   research services or to use a particular broker-dealer which MassMutual has
   recommended.
  
 6.  Representations And Warranties of The
   Sub-Adviser.
  
         The Sub-Adviser
   hereby represents and warrants to the Fund and MassMutual that:
  
 
  
   |  |         (a)  The
     Sub-Adviser has obtained all required governmental and regulatory
     licenses, registrations and approvals required by law as may be necessary
     to perform its obligations under this Sub-Advisory Agreement and to act as
     contemplated by the Trust Documents and the Disclosure Documents,
     including without limitation registration as an investment adviser under
     the Advisers Act, and will maintain and renew any required licenses,
     registrations, approvals and memberships during the term of this
     Sub-Advisory Agreement.
   
  
 
  
 
  
   |  |         (b) 
      There is no pending, or to the best of its knowledge, threatened or
     contemplated action, suit or proceeding before or by any court,
     governmental, administrative or self-regulatory body or arbitration panel
     to which the Sub-Adviser or any of its principals or affiliates is a
     party, or to which any of the assets of the Sub-Adviser is subject, which
     reasonably might be expected to (i) result in any material adverse change
     in the Sub-Adviser’s condition (financial or otherwise), business or
     prospects, (ii) affect adversely in any material respect any of the
     Sub-Adviser’s assets, or (iii) materially impair the
     Sub-Adviser’s ability to discharge its obligations under this
     Sub-Advisory Agreement; and the Sub-Adviser has not received any notice of
     an investigation by the Securities and Exchange Commission or any state
     regarding U.S. federal or state securities laws, regulations or rules
     other than routine examinations of the books and records of the
     Sub-Adviser.
   
  
 
  
 
  
   |  |         (c)  All
     references in the Disclosure Documents concerning the Sub-Adviser and its
     affiliates and the controlling persons, affiliates, stockholders,
     directors, officers and employees of any of the foregoing are accurate in
     all material respects and do not contain any untrue statement of a
     material fact or omit to state a material fact necessary in order to make
     such information not misleading.
   
  
 
  
         The foregoing
   representations and warranties shall be continuing during the term of this
   Sub-Advisory Agreement.
  
 7.  Covenants of the Sub-Adviser.
  
         (a)  If at
   any time during the term of this Sub-Advisory Agreement, the Sub-Adviser
   discovers any fact or omission, or any event or change of circumstances
   occurs, which would make the Sub-Adviser’s representations and
   warranties in Section 6 inaccurate or incomplete in any material respect, or
   which might render the Disclosure Documents untrue or misleading in any
   material respect, the Sub-Adviser will provide prompt written notification
   to the Fund and MassMutual of any such fact, omission, event or change of
   circumstances, and the facts related thereto.
  
         (b)  The
   Sub-Adviser agrees that, during the term of this Sub-Advisory Agreement, and
   for so long as investment in the Fund is being offered for sale, it will
   provide the Fund and the Sub-Adviser with updated information relating to
   the Sub-Adviser’s performance results as reasonably required from time
   to time by the Fund and MassMutual. The Sub-Adviser shall use its best
   efforts to provide such information within a reasonable period of time after
   the end of the month to which such updated information relates and the
   information is available to it.
  
 
           (c)  The
   Sub-Adviser or its delegated auditor will make available for review by
   MassMutual (and, if requested by MassMutual, its designated auditors or
   attorneys) all audited reports relating the Sub-Adviser’s composite
   performance results with respect to the Fund and other funds or accounts of
   the Sub-Adviser with substantially similar investment objectives and
   strategies and which are in the Sub-Adviser’s possession or to which it
   has access. Sub-Adviser will make its or its delegated auditor’s
   representatives available to discuss any items contained in such audited
   reports.
  
 8.  Confidentiality.
  
         All information and
   advice furnished by one party to the other party (including their respective
   agents, employees and representatives) hereunder shall be treated as
   confidential and shall not be disclosed to third parties, except as may be
   necessary to comply with applicable laws, rules and regulations, subpoenas
   or court orders.
  
 9.  Duration.
  
         Unless terminated
   earlier pursuant to Section 10 hereof, this Sub-Advisory Agreement shall
   remain in effect for a period of two years from the date hereof. Thereafter
   it shall continue in effect from year to year, unless terminated pursuant to
   Section 10 hereof, so long as such continuance shall be approved at least
   annually by the Trust’s Board of Trustees, including the vote of the
   majority of the Trustees of the Trust who are not parties to this
   Sub-Advisory Agreement or “interested persons” (as defined in the
   Act) of any such party cast in person at a meeting called for the purpose of
   voting on such approval, or by the holders of a “majority” (as
   defined in the Act) of the outstanding voting securities of the
   Fund.
  
 10.  Termination.
  
         (a)  This
   Sub-Advisory Agreement shall terminate automatically upon its unauthorized
   assignment (within the meaning of the Act), the termination of the Advisory
   Agreement or the dissolution of the Fund.
  
         (b)  The
   Sub-Advisory Agreement may be terminated by MassMutual or the Board of
   Trustees of the Trust: (i) by written notice to the Sub-Adviser with
   immediate effect, if the Sub-Adviser’s registration under the
   Adviser’s Act is suspended, terminated, lapsed or not renewed; (ii) by
   written notice to the Sub-Adviser with immediate effect, if the Sub-Adviser
   is bankrupt or insolvent, seeks an arrangement with creditors, is dissolved
   or terminated or ceases to exist; (iii) by written notice to the Sub-Adviser
   with immediate effect, if MassMutual determines in good faith, for any
   reason, that such termination is appropriate for the protection of the Fund,
   including without limitation a good faith determination by MassMutual or the
   Board of Trustees of the Trust that the Sub-Adviser has breached an
   obligation or duty under this Sub-Advisory Agreement; or (iv) in their sole
   discretion, without penalty, upon ninety days prior written notice to
   Sub-Adviser. This Sub-Advisory Agreement also may be terminated at any time,
   without penalty, by the vote of the holders of a “majority” of the
   outstanding voting securities of the Fund (as defined in the
   Act).
  
         (c)  The
   Sub-Advisory Agreement may be terminated by the Sub-Adviser, without penalty
   at any time, upon ninety days’ prior written notice, to MassMutual and
   the Trust.
  
 11.  Indemnification.
  
         (a)  In any
   action in which MassMutual or the Fund or any of its or their controlling
   persons, or any shareholders, partners, directors, officers and/or employees
   of any of the foregoing, are parties, the Sub-Adviser agrees to indemnify
   and hold harmless the foregoing persons against any loss, claim, damage,
   charge, liability or expense (including, without limitation, reasonable
   attorneys’ and accountants’ fees) to which such persons may become
   subject, insofar as such loss, claim, damage, charge, liability or expense
   arises out of or is based upon an act or omission of the Sub-Adviser or its
   officers, directors, employees, affiliates or controlling persons or the
   performance of the Sub-Adviser of its obligations hereunder constituting
   willful misfeasance, bad faith, gross negligence, fraud or willful
   misconduct.
  
 
           (b)  In any action
   in which the Sub-Adviser or any of its controlling persons, or any
   shareholders, partners, directors, officers and/or employees of any of the
   foregoing, are parties, MassMutual agrees to indemnify and hold harmless the
   foregoing persons against any loss, claim, settlement, damage, charge,
   liability or expense (including, without limitation, reasonable
   attorneys’ and accountants’ fees) to which such persons may become
   subject, insofar as such loss, claim, settlement, damage, charge, liability
   or expense arises out of or is based upon any demands, claims, liabilities,
   expenses, lawsuits, actions or proceedings relating to this Sub-Advisory
   Agreement, the advisory services for the account of the Fund provided by the
   Sub-Adviser, the operation of the Fund or the contents of the Disclosure
   Documents, provided that the loss, claim, damage, liability, cost or expense
   did not relate to, or was not based upon, or did not arise out of an act or
   omission of the Sub-Adviser, its shareholders, or any of its partners,
   officers, directors, employees, agents or controlling persons constituting
   willful misfeasance, bad faith, gross negligence, fraud, willful misconduct,
   or a breach of this Sub-Advisory Agreement.
  
         (c) 
    Promptly after receipt by an indemnified party under this Section 11
   of notice of any claim or dispute or commencement of any action or
   litigation, such indemnified party will, if a claim in respect thereof is to
   be made against an indemnifying party under this Section 11, notify the
   indemnifying party of the commencement thereof; but the omission to notify
   the indemnifying party will not relieve it from any liability which it may
   have to any indemnified party otherwise than under this Section 11 except to
   the extent, if any, that such failure or delay prejudiced the other party in
   defending against the claim. In case any such claim, dispute, action or
   litigation is brought or asserted against any indemnified party, and it
   notifies the indemnifying party of the commencement thereof, the
   indemnifying party will be entitled to participate therein and, to the
   extent that it may wish, to assume the defense thereof, with counsel
   specially approved in writing by such indemnified party, such approval not
   to be unreasonably withheld, following notice from the indemnifying party to
   such indemnified party of its election so to assume the defense thereof; in
   which event, the indemnifying party will not be liable to such indemnified
   party under this Section 11 for any legal or other expenses subsequently
   incurred by such indemnified party in connection with the defense thereof,
   but shall continue to be liable to the indemnified party in all other
   respects as heretofore set forth in this Section 11. Notwithstanding any
   other provisions of this Section 11, if, in any claim, dispute, action or
   litigation as to which indemnity is or may be available, any indemnified
   party reasonably determines that its interests are or may be, in whole or in
   part, adverse to the interests of the indemnifying party, the indemnified
   party may retain its own counsel, with the choice of counsel subject to the
   consent of the indemnifying party (which consent shall not be withheld
   unreasonably), in connection with such claim, dispute, action or litigation
   and shall continue to be indemnified by the indemnifying party for any legal
   or any other expenses reasonably incurred in connection with investigating
   or defending such claim, dispute, action or litigation.
  
 12.  Disclaimer of Shareholder
   Liability.
  
         MassMutual and the
   Sub-Adviser understand that the obligations of the Trust under this
   Sub-Advisory Agreement are not binding upon any Trustee or shareholder of
   the Trust personally, but bind only the Trust and the Trust’s property.
   MassMutual and the Sub-Adviser represent that each has notice of the
   provisions of the Trust Documents disclaiming shareholder and Trustee
   liability for acts or obligations of the Trust.
  
 13.  Notice.
  
         Any notice under this
   Sub-Advisory Agreement shall be in writing, addressed and delivered or
   mailed, postage prepaid, to the other party, with a copy to the Trust, at
   the addresses below or such other address as such other party may designate
   for the receipt of such notice.
  
         
 
  
   | If to MassMutual:
     
   
    |  |  | ▇▇▇▇ ▇▇▇▇▇
     ▇▇▇▇▇▇
   
  
 
 
  
   |  | ▇▇▇▇▇▇▇▇▇▇▇, ▇▇
     ▇▇▇▇▇
   
  
 
 
  
   |  | Attention:  ▇▇▇▇▇▇ ▇. ▇▇▇▇▇, Vice President
   
  
 
  
 
          
 
  
   |  If to the
     Sub-Adviser: 
   
    | RS Investment
     Management L.P.
   
  
  
    |  | ▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇,
     ▇▇▇▇▇ ▇▇▇
   
  
 
 
  
   |  | ▇▇▇ ▇▇▇▇▇▇▇▇▇, ▇▇
     ▇▇▇▇▇
   
  
 
 
  
   |  | Attention:  ▇▇▇▇▇ ▇▇▇▇▇▇▇
   
  
 
  
         If to either
   MassMutual or the Sub-Adviser, copies to:
  
  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |