MERRIMAC MASTER PORTFOLIO
POS AMI, 2000-04-28
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    As filed with the Securities and Exchange Commission on April 28, 2000


                          1940 Act File No. 811-07941

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                                   FORM N-1A

        REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940



                                AMENDMENT NO. 3



                           MERRIMAC MASTER PORTFOLIO
              (Exact Name of Registrant as Specified in Charter)

 P.O. Box 501, Cardinal Avenue, George Town, Grand Cayman, Cayman Islands, BWI
                   (Address of Principal Executive Offices)

      Registrant's Telephone Number, Including Area Code: (809) 949-2001


                          Susan C. Mosher, Secretary
                           Merrimac Master Portfolio
                             200 Clarendon Street
                                Mail Code LEG13
                          Boston, Massachusetts 02116
                    (Name and Address of Agent for Service)




                                    Copy to:
                               Philip H. Newman
                          Goodwin, Procter & Hoar LLP
                                Exchange Place
                          Boston, Massachusetts 02109








                                      (i)

<PAGE>




                           MERRIMAC MASTER PORTFOLIO

                               EXPLANATORY NOTE

This  Registration  Statement  has been  filed by the  Registrant  pursuant  to
Section  8(b) of the  Investment  Company  Act of 1940,  as amended  (the "1940
Act"). However, beneficial interests in the Registrant are not being registered
under the  Securities  Act of 1933,  as  amended  (the "1933  Act")  since such
interests will be issued solely in private placement  transactions which do not
involve any "public  offering"  within the meaning of Section  4(2) of the 1933
Act.  Investments  in the  Registrant's  series may only be made by "accredited
investors"  within  the  meaning  of  Regulation  D under  the 1933  Act  which
generally includes institutional investors and high net worth individuals. This
Registration   Statement   does  not  constitute  an  offer  to  sell,  or  the
solicitation of an offer to buy, any beneficial  interests in any series of the
Registrant.

Pursuant to General Instruction B2 of Form N-1A, a registration statement filed
under  only  the  1940 Act  shall  consist  of the  facing  sheet of the  Form,
responses to all items of Parts A and B except Items 1, 2, 3, 5 and 9 of Part A
thereof,  responses  to all items of Part C except  Items 23(e) and (i)-(k) and
the required signatures, and all other documents that are required or which the
Registrant may file as part of the registration statement.

                                     (ii)


<PAGE>






















                                    PART A





















                                     A - 1

<PAGE>



                                    PART A
                                   May l, 2000





Responses to Items 1, 2, 3, 5 and 9 have been omitted pursuant to paragraph (b)
of Instruction B.2. of the General Instructions to Form N-1A.

Item 4. INVESTMENT OBJECTIVE, PRINCIPAL INVESTMENT STRATEGIES AND RELATED RISKS

MERRIMAC CASH PORTFOLIO

INVESTMENT OBJECTIVE

The investment  objective of the Merrimac Cash Portfolio (the "Cash Portfolio")
is to  achieve  a high  level of  current  income  consistent  with  preserving
principal and liquidity.  In view of the risks  inherent in all  investments in
securities,  there is no  assurance  that  the  Portfolio's  objective  will be
achieved.

IMPLEMENTATION OF INVESTMENT OBJECTIVES

The Cash Portfolio is a series of the Merrimac Master Portfolio (the "Portfolio
Trust"),  an  open-end  management  investment  company  which is  treated as a
partnership for federal tax purposes.  Allmerica Asset Management, Inc. ("AAM")
acts as sub-adviser to the Cash Portfolio and manages its investment program.



The Cash Portfolio's  principal  investment  strategy is to invest,  indirectly
through the Cash Portfolio, its assets in high quality U.S. dollar-denominated,
money market instruments with remaining maturities of 397 calendar days or less
that in the opinion of AAM present minimal credit risk.

   The Cash  Portfolio  may invest in the  following  U.S.  dollar  denominated
   instruments:

   o  variable rate obligations;

   o  commercial  paper;

   o  corporate debt;

   o  certificates  of deposits;

   o  obligations of the U.S. Government or its agencies or instrumentalities;

   o  U.S. Treasury bills, notes and bonds,

   o  variable rate municipal obligation;

   o  municipal obligations;

   o  securities  of U.S.  and foreign banks or  thrift organizations  (such as
      bankers' acceptances, time deposits and certificates of deposits);

   o  time deposits;

   o  asset-backed securities;

   o  other short-term debt securities; and

   o  repurchase agreements that are collateralized by the securities listed
      above.



Further description of these securities is found in APPENDIX A.

                                     A - 2

<PAGE>

The Securities and Exchange  Commission  (SEC) has set certain  diversification
requirements  for money market funds.  Generally,  these  requirements  limit a
money market fund's  investments in securities of any issuer to no more than 5%
of a fund's  assets.  Also,  strict SEC guidelines do not permit AAM to invest,
with  respect to 75% of the Cash  Portfolio's  assets,  greater than 10% of the
Cash Portfolio's assets in securities issued by or subject to guarantees by the
same  institution.  Purchases of  securities  issued or  guaranteed by the U.S.
Government or its agencies or  instrumentalities  are not counted  toward these
limitations.

The Cash  Portfolio's  investments  consist  of  high-quality  securities  that
qualify  as  "first-tier"  securities  under the SEC rules  that apply to money
market funds. In general,  a first-tier  security is defined as a security that
is:



   o  issued  or   guaranteed   by  the  U.S.   Government  or  any  agency  or
      instrumentality thereof;
   o  rated or subject to a guarantee that is rated in the highest category for
      short-term securities by at least two Nationally  Recognized  Statistical
      Rating Organizations  (NRSROs),  or by one NRSRO if the security is rated
      by only one NRSRO;
   o  unrated but issued by an issuer or  guaranteed  by a  guarantor  that has
      other comparable short-term obligations so rated; or
   o  unrated  but  determined  by AAM to be of  comparable  quality  to  other
      first-tier securities.

In addition, AAM must consider whether a particular investment presents minimal
credit risk.

The current NRSROs are:



   o  Moody's Investors Service, Inc.;
   o  Standard & Poor's Ratings Group;
   o  Fitch's IBCA Investors Service;
   o  Duff & Phelps; and
   o  Thomson Bank Watch.

If the rating of a security is downgraded  after  purchase,  AAM will determine
whether it is in the best  interest  of the Cash  Portfolio's  shareholders  to
continue to hold the security.

While AAM will endeavor to maintain a constant NAV of $1 per share, there is no
assurance  that they will be able to do so. The shares are neither  insured nor
guaranteed by the U.S.  Government.  As such, the Cash  Portfolio  carries some
risk. For example, there is always a risk that the issuer of a security held by
the Cash  Portfolio  will fail to pay interest or principal  when due. The Cash
Portfolio  attempts to minimize  credit risk by  investing  only in  securities
rated in the highest category for short-term  securities,  or, if not rated, of
comparable quality, at the time of purchase.  Additionally,  the Cash Portfolio
will not  purchase  a  security  unless AAM has  determined  that the  security
presents  minimal credit risk.  There is also a risk that rising interest rates
will cause the value of the Cash  Portfolio's  securities to decline.  The Cash
Portfolio  attempts to minimize  interest rate risk by limiting the maturity of
each  security to 397 calendar days or less and  maintaining a  dollar-weighted
average portfolio maturity for the Cash Portfolio of 90 days or less.

In arriving at a decision to buy or sell a security,  factors are balanced such
as credit quality and maturity to purchase the best relative value available in
the market at any given time. While rare, sell decisions are usually based on a
change in credit analysis or to take advantage of an opportunity to reinvest at
a higher yield.

                                     A - 3

<PAGE>

MERRIMAC TREASURY PORTFOLIO

INVESTMENT OBJECTIVE

The  investment  objective of the Merrimac  Treasury  Portfolio  (the "Treasury
Portfolio")  is to  achieve a high  level of  current  income  consistent  with
preserving  principal  and  liquidity.  In view of the  risks  inherent  in all
investments in securities,  there is no assurance that the Treasury Portfolio's
objective will be achieved.

IMPLEMENTATION OF INVESTMENT OBJECTIVES

The  Treasury  Portfolio  is a  series  of the  Portfolio  Trust,  an  open-end
management investment company which is treated as a partnership for federal tax
purposes.  M&I Investment  Management Corp.  ("M&I") acts as sub-adviser to the
Treasury Portfolio and manages its investment program.



   The  Treasury  Portfolio's  principal  investment  strategy is to invest its
   assets in, U.S. Treasury  securities with maturities of 397 calendar days or
   less.

The  Treasury  Portfolio  will only  invest  indirect  obligations  of the U.S.
Treasury,  which are U.S.  Treasury  bills,  notes and bonds and in other money
market  mutual  funds  having the same  principal  investment  strategy.  Under
Federal law, the income derived from obligations issued by the U.S. Treasury is
exempt from state  income  taxes.  All states that tax personal  income  permit
mutual  funds to pass  through this tax  exemption  to  shareholders,  assuming
appropriate   state  imposed  threshold  limits  have  been  met.  To  maximize
tax-effective yield for shareholders,  under normal circumstances, the Treasury
Portfolio will only invest in  obligations  that qualify for the exemption from
state taxation.

While M&I will endeavor to maintain a constant NAV of $1 per share, there is no
assurance  that they will be able to do so. The shares are neither  insured nor
guaranteed by the U.S. Government. As such, the Treasury Portfolio carries some
risk.  There is a risk that rising  interest  rates will cause the value of the
Treasury Portfolio's  securities to decline. M&I attempts to minimize this risk
by limiting  the  maturity of each  security to 397  calendar  days or less and
maintaining  a  dollar-weighted  average  portfolio  maturity  for the Treasury
Portfolio of 90 days or less.

In arriving at a decision to buy or sell a security,  factors are balanced such
as the  Treasury  Portfolio's  objective  of  maximizing  current  income while
maintaining safety and liquidity.  M&I evaluates the treasury securities market
daily to determine how to provide the most value to the Treasury Portfolio.



MERRIMAC TREASURY PLUS PORTFOLIO

INVESTMENT OBJECTIVE

The investment objective of the Merrimac Treasury Plus Portfolio (the "Treasury
Plus  Portfolio") is to achieve a high level of current income  consistent with
preserving  principal  and  liquidity.  In view of the  risks  inherent  in all
investments  in  securities,  there  is no  assurance  that the  Treasury  Plus
Portfolio's objective will be achieved.

                                     A -4

<PAGE>

IMPLEMENTATION OF INVESTMENT OBJECTIVES

The Treasury  Plus  Portfolio is a series of the Portfolio  Trust,  an open-end
management investment company which is treated as a partnership for federal tax
purposes.  M&I acts as  sub-adviser  to the Treasury Plus Portfolio and manages
its investment program.

The Treasury Plus Portfolio's  principal  investment  strategy is to invest its
assets  in  high-quality,  U.S.  dollar-denominated  Treasury  securities  with
maturities of 397 calendar days or less.



The Treasury Plus Portfolio will invest at least 65% its total assets in direct
obligations of the U.S. Treasury (U.S.  Treasury bills, notes and bonds ) or in
repurchase  agreements  collateralized by these instruments.  It may invest the
remaining of assets in securities  issued or guaranteed by the U.S.  Government
or  its  agencies  or  in  repurchase   agreements   collateralized   by  these
instruments.



While M&I will endeavor to maintain a constant NAV of $1 per share, there is no
assurance  that they will be able to do so. The shares are neither  insured nor
guaranteed by the U.S. Government. As such, the Treasury Plus Portfolio carries
some risk.  There is a risk that rising  interest rates will cause the value of
the Treasury Plus Portfolio's  securities to decline.  M&I attempts to minimize
interest  rate risk by limiting the  maturity of each  security to 397 calendar
days or less and maintaining a dollar-weighted  average portfolio  maturity for
the Treasury Plus Portfolio of 90 days or less.

In arriving at a decision to buy or sell a security,  factors are balanced such
as the Treasury Plus Portfolio's  objective of maximizing  current income while
maintaining  safety and  liquidity.  M&I  evaluates the  government  securities
market compared to the repurchase  agreement market to determine which provides
the most value to the Treasury Plus Portfolio.

MERRIMAC U.S. GOVERNMENT PORTFOLIO

INVESTMENT OBJECTIVE

The investment  objective of the Merrimac U.S. Government  Portfolio (the "U.S.
Government  Portfolio") is to achieve a high level of current income consistent
with preserving  principal and liquidity.  In view of the risks inherent in all
investments  in  securities,  there is no  assurance  that the U.S.  Government
Portfolio's objective will be achieved.

IMPLEMENTATION OF INVESTMENT OBJECTIVES

The U.S.  Government  Portfolio is a series of the Portfolio Trust, an open-end
management investment company which is treated as a partnership for federal tax
purposes.  AAM acts as sub-adviser to the U.S. Government Portfolio and manages
its investment program.



The U.S. Government  Portfolio's principal investment strategy is to invest its
assets in high-quality,  U.S.  dollar-denominated money market instruments with
maturities of 397 calendar days or less.

The U.S.  Government  Portfolio will invest at least 65% of its total assets in
securities  issued or  guaranteed by the U.S.  Government or its agencies.  The
U.S.  Government  Portfolio also may invest in repurchase  agreements  that are
collateralized by these instruments. Further description of these securities is
found in APPENDIX A.



While AAM will endeavor to maintain a constant NAV of $1 per share, there is no
assurance  that they will be able to do so. The shares are neither  insured nor
guaranteed  by the U.S.  Government.  As such,

                                     A - 5

<PAGE>

the U.S.  Government  Portfolio  carries some risk. There is a risk that rising
interest  rates  will  cause  the  value  of the  U.S.  Government  Portfolio's
securities to decline.  AAM attempts to minimize interest rate risk by limiting
the maturity of each  security to 397 calendar  days or less and  maintaining a
dollar-weighted average portfolio maturity for the U.S. Government Portfolio of
90 days or less.

In arriving at a decision to buy or sell a security,  factors are balanced such
as the U.S. Government Portfolio's objective of maximizing current income while
maintaining  safety and  liquidity.  AAM  evaluates the  government  securities
market compared to the repurchase  agreement market to determine which provides
the most value to the U.S. Government Portfolio.

Item 6. MANAGEMENT, ORGANIZATION AND CAPITAL STRUCTURE

MANAGEMENT

INVESTMENT ADVISER

The Cash Portfolio, the Treasury Portfolio, the Treasury Plus Portfolio and the
U.S.   Government   Portfolio  (each  a  "Portfolio"  and   collectively,   the
"Portfolios") have each retained the services of Investors Bank & Trust Company
("Investors Bank") as investment adviser.  Investors Bank continuously  reviews
and supervises each Portfolio's  investment program.  Investors Bank discharges
its responsibilities subject to the supervision of, and policies established by
the Board of  Trustees.  Investors  Bank's  business  address is 200  Clarendon
Street,  Boston,  Massachusetts  02116.  Investors  Bank  began  acting  as  an
investment  adviser at the  commencement  of operations  of the Cash  Portfolio
(November 21, 1996).  The Portfolios  each pay Investors Bank a unitary fee for
services as Investment Adviser,  Administrator,  Custodian, Fund Accountant and
Transfer  Agent.  The fee is computed at an annual rate of 0.17% of average net
assets of each such Portfolio.



The investment  adviser and sub-advisers may pay out of their respective fees a
transaction,  service,  administrative,  or  other  similar  fee  charged  by a
financial intermediary,  or other financial  representative with respect to the
purchase or sale of shares of each Fund. The financial  intermediaries also may
impose  requirements on the purchase or sale of shares that are different from,
or in addition to, those imposed by each Fund, including requirements as to the
minimum initial and subsequent investment amounts.



INVESTMENT SUB-ADVISERS

AAM  serves  as  investment  sub-adviser  to the  Cash  Portfolio  and the U.S.
Government  Portfolio.  AAM manages the Cash Portfolio and the U.S.  Government
Portfolio,  selects investments and places all orders for the purchase and sale
of the Cash Portfolio and the U.S. Government Portfolio's  securities,  subject
to the  general  supervision  of,  and  policies  established  by the  Board of
Trustees and Investors Bank. The business address of AAM is 440 Lincoln Street,
Worcester,  Massachusetts  01653.  AAM has been providing  investment  advisory
services  since  it  was  established  in  1993  as an  indirect,  wholly-owned
subsidiary  of  Allmerica  Financial  Corporation.  AAM  receives  a  fee  from
Investors  Bank  (and  not  from the  Cash  Portfolio  or the  U.S.  Government
Portfolio)  for its services as investment  sub-adviser.  Prior to September 1,
1998,  The  Bank of New  York  acted  as  investment  sub-adviser  for the Cash
Portfolio.

M&I serves as investment sub-adviser to the Treasury Portfolio and the Treasury
Plus  Portfolio.  M&I manages the  Treasury  Portfolio  and the  Treasury  Plus
Portfolio,  selects investments and places all orders for the purchase and sale
of the Treasury Portfolio and the Treasury Plus Portfolio's securities, subject
to the  general  supervision  of,  and  policies  established  by the  Board of
Trustees and Investors  Bank.  The

                                     A - 6

<PAGE>

business address of M&I is 1000 North Water Street, Milwaukee, Wisconsin 53202.
M&I has been providing investment advisory services since it was established in
1973 as a first tier wholly-owned subsidiary of Marshall & Isley Corporation, a
publicly held bank holding company.  M&I receives fees from Investors Bank (and
not from  the  Treasury  Portfolio  or the  Treasury  Plus  Portfolio)  for its
services as investment sub-adviser.

Item 7. SHAREHOLDER INFORMATION

PRICING OF PORTFOLIO INTERESTS



An investment in any Portfolio may be made without a sales load. Securities are
valued at amortized cost,  which the Trustees of the Portfolios have determined
in good faith  constitutes  fair value for the purposes of  complying  with the
1940 Act. A Business  Day is any day on which both the New York Stock  Exchange
and the New York Federal  Reserve  Bank are open.  This  valuation  method will
continue to be used until such time as the Trustees of the Portfolios determine
that it does not constitute fair value for such purposes.



PURCHASE OF PORTFOLIO INTERESTS

Beneficial  interests in each Portfolio are issued solely in private  placement
transactions  which do not involve any "public  offering" within the meaning of
Section 4(2) of the 1933 Act. Investments in each Portfolio may only be made by
investment companies, insurance company separate accounts, common or commingled
trust  funds  or  similar  organizations  or  entities  which  are  "accredited
investors"  within  the  meaning  of  Regulation  D under  the 1933  Act.  This
Registration   Statement   does  not  constitute  an  offer  to  sell,  or  the
solicitation of an offer to buy, any "security"  within the meaning of the 1933
Act.

There  is no  minimum  initial  or  subsequent  investment  in the  Portfolios.
However, since the Portfolios intend to be as fully invested at all times as is
reasonably  practicable  in  order  to  enhance  the  yield  on  their  assets,
investments must be made in federal funds (i.e., monies credited to the account
of a Portfolio's custodian bank by a Federal Reserve Bank).

Each Portfolio reserves the right to cease accepting investments at any time or
to reject any investment order.

REDEMPTION OF PORTFOLIO INTERESTS

Shares of a  Portfolio  are not  registered  under the 1933 Act and are sold in
reliance upon an exemption from registration.  Shares may not be transferred or
resold without registration under the 1933 Act, except pursuant to an exemption
from registration. However, shares may be redeemed on any Business Day.

MASTER FEEDER FUNDS

"Feeder" funds invest exclusively in their  corresponding  "master"  portfolios
with  identical  investment   objectives.   The  master  portfolio  may  accept
investments  from  multiple  feeder  funds,  which bear the master  portfolio's
expenses in proportion to their assets.



Each  feeder  fund and its  master  portfolio  expect  to  maintain  consistent
investment objectives, but if they do not, a fund will withdraw from the master
portfolio,  receiving either cash or securities in exchange for its interest in
the master  portfolio.  The  trustees  of the trust of a feeder fund would then
consider  whether

                                     A - 7

<PAGE>

a fund should hire its own investment adviser, invest in a different portfolio,
or take other action.



                                     A - 8

<PAGE>

                                  APPENDIX A

MONEY MARKET  INSTRUMENTS.  An investment in a Portfolio is subject to interest
rate risk and credit risk of the issuers of the money market  instruments.  All
money market instruments can change in value when interest rates or an issuer's
creditworthiness  changes,  or if an issuer or guarantor of a security fails to
pay interest or principal when due.

U.S. GOVERNMENT SECURITIES. The Cash Portfolio, the Treasury Plus Portfolio and
the U.S. Government  Portfolio each may invest in U.S.  Government  Securities.
Not all U.S.  Government  Securities are backed by the full faith and credit of
the United States.  For example,  securities  issued by the Federal Farm Credit
Bank or by the Federal  National  Mortgage  Association  are  supported  by the
agency's   right  to  borrow  money  from  the  U.S.   Treasury  under  certain
circumstances.  Securities  issued by the Federal Home Loan Bank are  supported
only  by the  credit  of the  agency.  There  is no  guarantee  that  the  U.S.
Government  will support these types of securities,  and therefore they involve
more risk than "full  faith and credit"  Government  Securities.  The  Treasury
Portfolio  will  primarily  invest in "full faith and credit"  U.S.  Government
Securities.

BANKERS'  ACCEPTANCES.  The Cash  Portfolio may invest in bankers'  acceptances
which  are  bills  of  exchange  or time  drafts  drawn  on and  accepted  by a
commercial  bank.  They are used by  corporations  to finance the  shipment and
storage of goods and to furnish dollar  exchange.  Maturities are generally six
months or less.



COMMERCIAL PAPER. The Cash Portfolio may invest in commercial  paper,  which is
the term used to  designate  unsecured  short-term  promissory  notes issued by
corporations  and other  entities.  The Cash Portfolio may invest in commercial
paper  with  maturities  which  vary from a few days to nine  months.  The Cash
Portfolio  may also  purchase  U.S.  dollar-denominated  commercial  paper of a
foreign issuer rated in the highest or second  highest rating  categories by at
least two NRSROs.

SECURITIES  LENDING.  Each Portfolio may lend up to 33 1/3% of its portfolio of
securities  pursuant  to  agreements  requiring  that the loan be  continuously
secured  by cash or  equivalent  collateral  or by a letter  of  credit or bank
guarantee in favor of the  Portfolio at least equal at all times to 100% of the
market value plus accrued  interest on the securities  lent. The Portfolio will
continue  to receive  interest  on the  securities  lent  while  simultaneously
seeking to earn interest on the  investment of cash  collateral.  Collateral is
marked to market daily.  Loans are subject to  termination  by the Portfolio or
the  borrower at any time and are,  therefore,  not  considered  to be illiquid
investments.



TIME DEPOSITS.  The Cash Portfolio may invest in time deposits  ("TDs"),  which
are  non-negotiable  receipts  issued by a bank in exchange  for the deposit of
funds.  Like a certificate of deposit,  a TD earns a specified rate of interest
over a definite period of time;  however,  it cannot be traded in the secondary
market.



CERTIFICATES OF DEPOSIT.  The Cash Portfolio also may invest in certificates of
deposit  ("CDs"),  which are negotiable  interest  bearing  instruments  with a
specific maturity.  CDs are issued by banks and thrift institutions in exchange
for the deposit of funds and  normally  can be traded in the  secondary  market
prior to maturity.



CORPORATE  DEBT  OBLIGATIONS.  Subject to its  respective  credit  quality  and
maturity  limitations,  the Cash  Portfolio  may  invest  in  corporate  bonds,
including  obligations  of  industrial,  utility,  banking and other  financial
issuers.  Corporate  bonds are subject to the risk of an issuer's  inability to
meet principal and

                                     A - 9

<PAGE>

interest  payments  and may also be  subject  to price  volatility  due to such
factors as market interest rates, market perception of the credit worthiness of
the issuer and general market liquidity.

ASSET-BACKED  SECURITIES.  The Cash Portfolio  also may invest in  asset-backed
securities,  which consist of securities secured by company  receivables,  home
equity loans, truck and auto loans,  leases,  credit card receivables and other
securities backed by other types of receivables or other assets. Credit support
for  asset-backed  securities  may be based  on the  underlying  assets  and/or
provided  through  credit  enhancements  such as letters  of credit,  insurance
bonds,  limited  issuer  guarantees,  senior-subordinated  structures  and over
collateralization. Asset-backed securities are normally traded over-the-counter
and typically have a  short-intermediate  maturity  structure  depending on the
paydown  characteristics  of the underlying  financial  assets which are passed
through  to the  security  holder.  Asset-backed  securities  may be subject to
prepayment  risk,  particularly  in  a  period  of  declining  interest  rates.
Prepayments,  which occur when unscheduled  payments are made on the underlying
debt instruments,  may shorten the effective maturities of these securities and
may lower their total returns.  Asset-backed  securities  generally do not have
the benefit of a security interest in collateral that is comparable to mortgage
assets and there is the possibility  that recoveries on repossessed  collateral
may not be available to support payments on these securities. There is no limit
on the extent to which the  Portfolio  may invest in  asset-backed  securities;
however, the Portfolio will only invest in asset-backed securities that carry a
rating in the highest category from at least two NRSROs.

EURODOLLAR  AND YANKEE  DOLLAR  INVESTMENTS.  The Cash  Portfolio may invest in
Eurodollar and Yankee Dollar instruments.  Eurodollar  instruments are bonds of
foreign  corporate  and  government  issuers that pay interest and principal in
U.S.  dollars  held in banks  outside the United  States,  primarily in Europe.
Yankee Dollar instruments are U.S. dollar denominated bonds typically issued in
the U.S.  by foreign  governments  and their  agencies  and  foreign  banks and
corporations.  The Portfolio may invest in Eurodollar  Certificates  of Deposit
("ECDs"),  Eurodollar Time Deposits ("ETDs") and Yankee Certificates of Deposit
("Yankee CDs"). ECDs are U.S. dollar-denominated certificates of deposit issued
by  foreign  branches  of  domestic  banks;  ETDs are  U.S.  dollar-denominated
deposits in a foreign  branch of a U.S. bank or in a foreign  bank;  and Yankee
CDs are U.S. dollar-denominated certificates of deposit issued by a U.S. branch
of a foreign bank and held in the U.S. These investments involve risks that are
different from  investments  in securities  issued by U.S.  issuers,  including
potential unfavorable political and economic developments,  foreign withholding
or other  taxes,  seizure  of foreign  deposits,  currency  controls,  interest
limitations or other  governmental  restrictions  which might affect payment of
principal or interest.

WHEN-ISSUED  AND DELAYED  DELIVERY  TRANSACTIONS.  Each Portfolio may invest in
when-issued and delayed delivery securities, which are securities purchased for
delivery beyond the normal settlement date at a stated price and yield, thereby
involving the risk that the yield  obtained will be less than that available in
the market at delivery.  Although the purchase of  securities  on a when-issued
basis is not considered leveraging, it has the effect of leveraging.  When such
a security is purchased, the Custodian will set aside cash or liquid securities
to satisfy the purchase  commitment  unless the relevant  Portfolio has entered
into  an  offsetting  agreement  to  sell  the  securities.   These  segregated
securities  will be valued at market and additional  cash or securities will be
segregated  if necessary so that the market value of the account will  continue
to satisfy the purchase commitment. A Portfolio generally will not pay for such
securities or earn  interest on them until  received.  Commitments  to purchase
when-issued securities will not, under normal market conditions,  exceed 25% of
the  Portfolio's  total  assets,  and a  commitment  will not exceed 90 days. A
Portfolio  will  only  purchase  when-issued  securities  for  the  purpose  of
acquiring  portfolio  securities and not for speculative  purposes.  However, a
Portfolio  may sell these  securities or dispose of the  commitment  before the
settlement date if it is deemed advisable as a matter of investment

                                    A - 10

<PAGE>

strategy.  The market value of when-issued or delayed delivery  securities when
they are delivered may be less than the amount the Portfolios paid for them.

VARIABLE AND FLOATING RATE INSTRUMENTS. Certain of the obligations purchased by
each Portfolio may carry variable or floating rates of interest and may include
variable rate master demand  notes.  A floating rate security  provides for the
automatic  adjustment of its interest  rate whenever a specified  interest rate
changes. A variable rate security provides for the automatic establishment of a
new interest  rate on set dates.  Variable and floating  rate  instruments  may
include  variable  amount  master  demand  notes that  permit the  indebtedness
thereunder  to vary in addition to providing  for periodic  adjustments  in the
interest  rate.  There may be no active  secondary  market  with  respect  to a
particular  variable or floating rate  instrument.  Nevertheless,  the periodic
readjustments  of their  interest  rates tend to assure  that their  value to a
Portfolio  will  approximate  their  par  value.  Further,  some of the  demand
instruments purchased by a Portfolio derive their liquidity from the ability of
the holder to demand  repayment from the issuer or from a third party providing
credit support.  The  creditworthiness of issuers of variable and floating rate
instruments  and  their  ability  to  repay  principal  and  interest  will  be
continuously monitored by each Portfolio's investment adviser or sub-adviser.

REPURCHASE AGREEMENTS.  The Cash Portfolio, the Treasury Plus Portfolio and the
U.S. Government Portfolio each may enter into repurchase agreements,  which are
agreements by which a person obtains a security and  simultaneously  commits to
return the security to the seller at an agreed upon price (including  principal
and  interest)  on an agreed upon date within a number of days from the date of
purchase.  In  substance,  a repurchase  agreement  is a loan by the  Portfolio
collateralized with securities.  The lending Portfolio's Custodian or its agent
will  hold  the  security  as  collateral  for the  repurchase  agreement.  All
repurchase  transactions must be  collateralized  initially at a value at least
equal to 102% of the  repurchase  price  and  counterparties  are  required  to
deliver  additional  collateral in the event the market value of the collateral
falls below 100%. The  Portfolios  bear the risk of loss in the event the other
party  defaults on its  obligations  and the  Portfolio is delayed or prevented
from its right to  dispose of the  collateral  securities  or if the  Portfolio
realizes a loss on the sale of the collateral  securities.  Each Portfolio will
enter into repurchase agreements with financial  institutions deemed to present
minimal risk of bankruptcy during the term of the agreement based on guidelines
established and periodically reviewed by the Trustees.  Each Portfolio will not
invest  more than 10% of its net assets in  repurchase  agreements  maturing in
more than seven days  because such  agreements  would be  considered  "illiquid
securities."

REVERSE REPURCHASE AGREEMENTS.  The Cash Portfolio, the Treasury Plus Portfolio
and the U.S. Government  Portfolio each may borrow funds for temporary purposes
by entering into reverse  repurchase  agreements.  Pursuant to such agreements,
each  Portfolio  would sell the  securities to financial  institutions  such as
banks and broker-dealers and agree to repurchase them at a mutually agreed-upon
date and price. Each Portfolio will enter into reverse repurchase agreements to
avoid otherwise  selling  securities  during  unfavorable  market conditions to
provide cash to satisfy redemption requests.  At the time each Portfolio enters
into a reverse repurchase  agreement,  it would place in a segregated custodial
account,  assets  such as cash  or  liquid  securities,  consistent  with  each
Portfolio's investment  restrictions and having a value equal to the repurchase
price (including accrued interest),  and would subsequently monitor the account
to  ensure  that  such  equivalent  value was  maintained.  Reverse  repurchase
agreements  involve the risk that the  counterparty  may default at a time when
the market value of securities  sold by each Portfolio have increased in value.
Reverse repurchase agreements are considered by the SEC to be borrowings by the
Portfolio under the 1940 Act.

RESTRICTED AND ILLIQUID SECURITIES.  Each Portfolio may invest up to 10% of its
net assets in illiquid  securities.  Illiquid securities are those that are not
readily  marketable,  repurchase  agreements  maturing in

                                    A - 11

<PAGE>

more than seven days, time deposits with a notice or demand period of more than
seven days and certain restricted  securities.  Based upon continuing review of
the trading  markets for a specific  restricted  security,  the security may be
determined to be eligible for resale to qualified institutional buyers pursuant
to Rule 144A under the  Securities  Act of 1933 and,  therefore,  to be liquid.
Also,  certain  illiquid  securities may be determined to be liquid if they are
found to satisfy certain relevant liquidity requirements. The Board of Trustees
of  the  Portfolio  Trust  have  adopted   guidelines  and  delegated  to  each
Portfolio's  investment  adviser  or  sub-adviser,  as  applicable,  the  daily
function of determining  and monitoring the liquidity of portfolio  securities,
including  restricted  and  illiquid  securities.  Each  Portfolio's  Board  of
Trustees,  however,  retains  oversight and is ultimately  responsible for such
determinations.  The  purchase  price  and  subsequent  valuation  of  illiquid
securities  normally  reflect a discount,  which may be  significant,  from the
market price of comparable securities for which a liquid market exists.

SHORT-TERM TRADING.  Although each Portfolio usually intends to hold securities
purchased until  maturity,  at which time they will be redeemable at their full
principal value plus accrued interest, they may, at times, engage in short-term
trading to attempt to take  advantage  of yield  variations  in the  short-term
market.  Each Portfolio also may sell  portfolio  securities  prior to maturity
based on a revised evaluation of the  creditworthiness of the issuer or to meet
redemptions.  In the event there are unusually heavy redemption requests due to
changes in interest rates or otherwise,  a Portfolio may have to sell a portion
of its investment  portfolio at a time when it may be disadvantageous to do so.
However,   each  Portfolio  believes  that  its  ability  to  borrow  funds  to
accommodate  redemption  requests may mitigate in part the  necessity  for such
portfolio sales during these periods.

ZERO  COUPON  SECURITIES.   The  Cash  Portfolio  may  invest  in  zero  coupon
securities.  Zero coupon  securities are  securities  sold at a discount to par
value  and on  which  interest  payments  are not made  during  the life of the
security. Upon maturity, the holder is entitled to receive the par value of the
security.  The  Portfolio  is required to accrue  income with  respect to these
securities  prior to the  receipt  of cash  payments.  Because  the  Fund  will
distribute its share of this accrued income to shareholders, to the extent that
the  shareholders  and  shareholders  of other  mutual funds that invest in the
Portfolio  elect to receive  dividends  in cash  rather than  reinvesting  such
dividends in additional shares, the Portfolio will have fewer assets with which
to purchase income producing securities.  The Treasury Portfolio,  the Treasury
Plus  Portfolio  and the U.S.  Government  Portfolio  may invest in zero coupon
treasury securities.

LOAN  PARTICIPATIONS.  The Cash  Portfolio  may invest in loan  participations,
which represent a participation  in a corporate loan of a commercial bank. Such
loans must be to  corporations  in whose  obligations  the Cash  Portfolio  may
invest.  Since the issuing bank does not  guarantee the  participations  in any
way,  they are  subject  to the  credit  risks  generally  associated  with the
underlying corporate borrower.  It may be necessary under the terms of the loan
participation  for the Cash  Portfolio to assert  through the issuing bank such
rights as may exist against the corporate borrower, in the event the underlying
corporate  borrower  fails to pay  principal  and  interest  when due.  In such
circumstances,  the Cash Portfolio may be subject to delays, expenses and risks
that are greater than if the Cash  Portfolio had purchased a direct  obligation
(such as commercial  paper) of such borrower.  Further,  under the terms of the
loan  participation,  the Cash  Portfolio  may be regarded as a creditor of the
issuing bank (rather than the underlying corporate borrower),  so that the Cash
Portfolio  may also be  subject  to the risk that the  issuing  bank may become
insolvent.  The secondary market for loan  participations is extremely limited,
and therefore loan participations purchased by the Cash Portfolio are generally
regarded as illiquid.

                                    A - 12

<PAGE>

























                                    PART B



















                                     B - 1

<PAGE>

ITEM 10.        COVER PAGE AND TABLE OF CONTENTS


                           MERRIMAC MASTER PORTFOLIO
                            Merrimac Cash Portfolio
                          Merrimac Treasury Portfolio
                       Merrimac Treasury Plus Portfolio
                      Merrimac U.S. Government Portfolio

                                    PART B

                      STATEMENT OF ADDITIONAL INFORMATION



                                  May 1, 2000


This  Statement of Additional  Information  ("SAI") is not a Prospectus  and is
only authorized for  distribution  when preceded or accompanied by the Merrimac
Master  Portfolio's  (the  "Trust")  current  Prospectus  dated  May  1,  2000.
Financial  Statements  are  incorporated  by  reference  into this SAI from the
Trust's most recent Annual Report.  This SAI  supplements and should be read in
conjunction with the Prospectus, a copy of which may be obtained without charge
by calling the Trust at  1-888-MERRMAC  or writing  the Trust at 200  Clarendon
Street, Boston,  Massachusetts 02116. This SAI is not an offer of any Portfolio
for which an investor has not received a Prospectus.

Information  about the Funds' (including the SAI) may be reviewed and copied at
the SEC's Public Reference Room in Washington,  D.C., or you may obtain copies,
upon payment of a duplicating  fee, by writing to the Public  Reference Room of
the SEC, Washington,  D.C. 20549-0102 or by electronic request at the following
E-mail address: [email protected]. You may obtain information on the operation
of the Public  Reference Room by calling the SEC at  202-942-8090.  Reports and
other information  about the Fund may be obtained on the Commission's  Internet
site at http://www.sec.gov.



                               TABLE OF CONTENTS



                                Page                                       Page

Portfolio History                3      Capital Stock and Other Securities  12
Description of the Portfolios,
    Their Investments and Risks  3      Purchase, Redemption and Valuation  13
                                            of Shares

Management of the Trust          6      Taxation of the Trust               14

Control Persons and Principal    8      Calculation of Performance Data     16
    Holders of Securities

Investment Advisory and Other    9      Financial Statements                17
    Services

Brokerage Allocation and Other   11     Appendix                            18
    Practices



                                     B - 2

<PAGE>

ITEM 11.  PORTFOLIO HISTORY

The  Merrimac  Master  Portfolio  (the  "Portfolio  Trust") is composed of four
series: Merrimac Cash Portfolio ("Cash Portfolio"), Merrimac Treasury Portfolio
("Treasury  Portfolio"),  Merrimac  Treasury  Plus  Portfolio  ("Treasury  Plus
Portfolio")  and  Merrimac  U.S.   Government   Portfolio   ("U.S.   Government
Portfolio") (each, a "Portfolio" and collectively, the "Portfolios").

The Portfolio Trust is a common law trust organized under the laws of the State
of New York  pursuant  to a  Declaration  of Trust  dated  October 30, 1996 and
amended February 6, 1997, October 26, 1998 and March 15, 1999.

ITEM 12.  DESCRIPTION OF THE PORTFOLIOS, THEIR INVESTMENTS AND RISKS

CLASSIFICATION

Each Portfolio is a diversified  open-end,  management investment company under
the 1940 Act and a separate series of the Trust.

INVESTMENT STRATEGIES AND RISKS



MATURITY  AND  DURATION.  Duration  of an  individual  portfolio  security is a
measure of the security's price  sensitivity  taking into account expected cash
flow  and  prepayments  under a wide  range  of  interest  rate  scenarios.  In
computing  the  duration a  Portfolio  will have to  estimate  the  duration of
obligations  that are subject to  prepayment or redemption by the issuer taking
into account the influences of interest rates on prepayments and coupon flows.

Each of the Portfolios has a policy of investing in instruments with maturities
of 397 days or less. For purposes of complying with this policy, each Portfolio
will   determine  the  maturity  of  an  instrument  in  accordance   with  the
requirements  of Rule 2a-7 under the 1940 Act. Rule 2a-7 permits each Portfolio
to shorten the maturity of a particular  instrument in  circumstances  in which
the instrument is subject to certain types of demand features or  interest-rate
reset provisions.

EXCHANGE COMMERCIAL NOTES ("ECNs"). The Cash Portfolio may invest in ECNs. ECNs
are  short-term (90 days or less)  securities  that  automatically  extend to a
390-day maximum  maturity if the issuer does not redeem the ECNs on the Initial
Redemption Date (the equivalent of a commercial paper maturity).  The extension
feature  substitutes for bank back-up.  Investors  receive a premium for giving
the  issuer the option to extend the  maturity.  However,  investors  receive a
sizeable  additional  premium if the maturity is extended.  ECNs carry the same
credit rating(s) as the issuer's commercial paper.

FUNDING  AGREEMENTS.  The Cash  Portfolio may invest in funding  agreements.  A
funding  agreement is, in substance,  an obligation of indebtedness  negotiated
privately  between an investor and an  insurance  company.  Funding  agreements
often have  maturity-shortening  features,  such as an unconditional  put, that
permit the investor to require the  insurance  company to return the  principal
amount of the funding  agreement,  together with accrued  interest,  within one
year or less. Most funding agreements are not transferable by the investor and,
therefore, are illiquid,  except to the extent the funding agreement is subject
to a demand feature of seven days or less. An insurance  company may be subject
to special protections under state insurance laws, which protections may impair
the ability of the  investor to require  prompt  performance  by the  insurance
company of its payment obligations under the funding agreement.

                                     B - 3

<PAGE>

MONEY  MARKET   INSTRUMENTS  AND  REPURCHASE   AGREEMENTS.   The  money  market
instruments  in which  the  Cash  Portfolio  invests  include  short-term  U.S.
Government  Securities  (defined  below),  commercial paper  (promissory  notes
issued by corporations to finance their  short-term  credit needs),  negotiable
certificates  of  deposit,   non-negotiable   fixed  time  deposits,   bankers'
acceptances and repurchase  agreements.  The Treasury Portfolio invests only in
direct  obligations of the U.S.  Treasury.  The Treasury Plus Portfolio invests
substantially all of its assets in direct  obligations of the U.S. Treasury and
in U.S. Government Securities (defined below)and in repurchase agreements.



U.S.  Government  Securities include securities which are direct obligations of
the U.S.  Government  backed by the full faith and credit of the United States,
and securities issued by agencies and instrumentalities of the U.S. Government,
which may be guaranteed by the U.S. Treasury or supported by the issuer's right
to borrow from the U.S.  Treasury or may be backed by the credit of the federal
agency or instrumentality  itself.  Agencies and  instrumentalities of the U.S.
Government  include,  but are not limited to,  Federal Land Banks,  the Federal
Farm Credit  Bank,  the Central  Bank for  Cooperatives,  Federal  Intermediate
Credit  Banks,  Federal  Home Loan  Banks  and the  Federal  National  Mortgage
Association ("FNMA").

A repurchase  agreement is an agreement under which a Portfolio  acquires money
market  instruments  (generally U.S.  Government  Securities) from a commercial
bank, broker or dealer, subject to resale to the seller at an agreed-upon price
and date  (normally  the next  business  day).  The resale  price  reflects  an
agreed-upon  interest rate effective for the period the instruments are held by
a Portfolio  and is  unrelated  to the interest  rate on the  instruments.  The
instruments  acquired by a Portfolio  (including accrued interest) must have an
aggregate  market  value in excess of the resale  price and will be held by the
custodian  bank for the  Portfolio  until  they are  repurchased.  The Board of
Trustees of the Portfolio  Trust will monitor the standards that the investment
adviser or sub-adviser will use in reviewing the  creditworthiness of any party
to a repurchase agreement with a Portfolio.  See "Investment Advisory Services"
for information regarding the investment adviser and sub-adviser.

The use of repurchase  agreements  involves certain risks. For example,  if the
seller defaults on its obligation to repurchase the  instruments  acquired by a
Portfolio at a time when their market value has declined, a Portfolio may incur
a  loss.  If  the  seller  becomes  insolvent  or  subject  to  liquidation  or
reorganization  under  bankruptcy or other laws, a court may determine that the
instruments  acquired by a Portfolio are  collateral  for a loan by a Portfolio
and therefore are subject to sale by the trustee in bankruptcy.  Finally, it is
possible that a Portfolio may not be able to  substantiate  its interest in the
instruments  it  acquires.  It is expected  that these risks can be  controlled
through careful documentation and monitoring.

"WHEN-ISSUED" AND "DELAYED DELIVERY"  SECURITIES.  Each Portfolio may invest in
securities  purchased on a

                                     B - 4

<PAGE>

"when-issued" or "delayed delivery" basis.  Delivery and payment for securities
purchased on a when-issued  or delayed  delivery basis will normally take place
15 to 45 days after the date of the  transaction.  The payment  obligation  and
interest rate on the securities  are fixed at the time that a Portfolio  enters
into the commitment, but interest will not accrue to a Portfolio until delivery
of and payment for the securities.  Although each such Portfolio will only make
commitments to purchase  "when-issued" and "delayed  delivery"  securities with
the intention of actually  acquiring the  securities,  each such  Portfolio may
sell the  securities  before the settlement  date if deemed  advisable by their
investment adviser or sub-adviser.  Each Portfolio may also, with respect to up
to 25% of its total assets,  enter into contracts to purchase  securities for a
fixed price at a future date beyond customary settlement time.

Unless the  Portfolios  have entered into an  offsetting  agreement to sell the
securities  purchased on a "when-issued" or "forward commitment" basis, cash or
liquid  obligations  with a market  value equal to the amount of a  Portfolio's
commitment will be segregated with a Portfolio's  custodian bank. If the market
value of these  securities  declines,  additional  cash or  securities  will be
segregated  daily  so  that  the  aggregate  market  value  of  the  segregated
securities equals the amount of a Portfolio's commitment.

Securities purchased on a "when-issued" and "delayed delivery" basis may have a
market  value on delivery  which is less than the amount  paid by a  Portfolio.
Changes  in  market  value may be based  upon the  public's  perception  of the
creditworthiness  of the  issuer or  changes  in the level of  interest  rates.
Generally,   the  value  of  "when-issued,"  "delayed  delivery"  and  "forward
commitment"  securities will fluctuate  inversely to changes in interest rates,
i.e.,  they will  appreciate in value when interest rates fall and will decline
in value when interest rates rise.

PORTFOLIO POLICIES

The Portfolios  have adopted the following  fundamental  policies.  Each of the
Portfolio's  fundamental  policies  cannot  be  changed  unless  the  change is
approved by a "vote of the outstanding  voting  securities" of a Portfolio,  as
the case may be,  which  phrase as used  herein  means the lesser of (i) 67% or
more of the voting  securities  of a  Portfolio  present  at a meeting,  if the
holders of more than 50% of the  outstanding  voting  securities of a Portfolio
are present or represented by proxy,  or (ii) more than 50% of the  outstanding
voting securities of a Portfolio.

As a matter of fundamental policy, the Cash Portfolio,  the Treasury Portfolio,
the Treasury Plus Portfolio and the U.S. Government Portfolio may not:

         (1)  purchase  any  securities  that would  cause more than 25% of the
         total  assets  of the  Portfolio  at the time of such  purchase  to be
         invested  in  securities  of  one or  more  issuers  conducting  their
         principal  business  activities  in the same  industry,  provided that
         there is no limitation with respect to U.S.  Government  Securities or
         (for the Cash  Portfolio,  the Treasury  Plus  Portfolio  and the U.S.
         Government   Portfolio)  bank  obligations  or  repurchase  agreements
         collateralized by any of such obligations as applicable;

         (2) borrow money,  except as a temporary  measure for extraordinary or
         emergency  purposes  or  to  facilitate  redemptions,   provided  that
         borrowing  does not exceed an amount  equal to 33 1/3% of the  current
         value  of  the  Portfolio's   assets  taken  at  market  value,   less
         liabilities, other than borrowings;

         (3)  purchase  securities  on margin  (except for delayed  delivery or
         when-issued  transactions or such short-term  credits as are necessary
         for the clearance of transactions);

         (4) make  loans to any  person or firm;  provided,  however,  that the
         making  of  a  loan  shall  not  include   entering  into   repurchase
         agreements,  and  provided  further  that a  Portfolio  may  lend  its
         portfolio   securities  to  broker-dealers   or  other   institutional
         investors if the  aggregate  value of all  securities  loaned does not
         exceed 33 1/3% of the value of a Portfolio's total assets;

         (5) engage in the business of  underwriting  the securities  issued by
         others,  except that a Portfolio  will not be deemed to be engaging in
         the business of  underwriting  with respect to the purchase or sale of
         securities   subject   to  legal  or   contractual   restrictions   on
         disposition;

         (6) issue senior  securities,  except as  permitted by its  investment
         objective,  policies and restrictions,  and except as permitted by the
         1940 Act; and

                                     B - 5

<PAGE>

         (7) purchase or sell real estate,  commodities, or commodity contracts
         unless  acquired as a result of ownership of securities,  and provided
         further  that a  Portfolio  may  invest in  securities  backed by real
         estate and in financial futures contracts and options thereon.

If any  percentage  restriction  described  above is  adhered to at the time of
investment,  a subsequent increase or decrease in the percentage resulting from
a change in the net assets of the Portfolios will not constitute a violation of
the restriction.

ITEM 13.        MANAGEMENT OF THE TRUST

BOARD OF TRUSTEES

Overall  responsibility  for management and supervision of the Trust rests with
the Board of Trustees.  The Trustees approve all significant agreements between
the Trust and the persons and  companies  that  furnish  services to the Trust,
including  agreements with its custodian,  transfer agent,  investment adviser,
sub-adviser  and  administrator.   The  SAI  contains  background   information
regarding each of the Trustees and executive officers of the Trust.

TRUSTEES AND OFFICERS.  The names,  dates of birth and principal  occupation(s)
during the last five years of the  Trustees  and  officers of the Trust and the
Portfolio  Trust are listed below.  An asterisk (*) indicates that a Trustee is
an "interested  person" of the Trust and the Portfolio Trust, as defined in the
1940 Act.  The  business  address of the Trustees and officers of the Trust and
the Portfolio Trust is 200 Clarendon Street, Boston, Massachusetts 02116.

                                     B - 6

<PAGE>

TRUSTEES AND OFFICERS OF THE PORTFOLIO TRUST



KEVIN J. SHEEHAN, TRUSTEE*, 6/22/51, Director since 1990, President June 1992 -
present,  Chairman and Chief Executive  Officer June 1995 - present,  Investors
Bank & Trust Company, Chairman and Chief Executive Officer June 1995 - present,
Investors Financial Services Corp.

FRANCIS J. GAUL, JR., TRUSTEE,  9/25/43,  Private Investor July 1998 - present,
Director and Principal,  Triad Investment  Management  Company June 1997 - June
1998,  Vice  President,   Triad  Investment   Management  Company   (Registered
Investment  Adviser) July 1996 - May 1997,  Vice President & Resident  Manager,
Goldman  Sachs & Co.  (Investment  Banking &  Institutional  Sales) June 1993 -
January 1995.



EDWARD F. HINES, JR., TRUSTEE,  9/5/45, Partner 1977 - present,  Choate, Hall &
Stewart.

THOMAS E. SINTON,  TRUSTEE,  8/26/32,  Retired,  Managing  Director,  Corporate
Accounting  Policy,  April 1993 - October 1996 and  Consultant,  January 1993 -
March 1996, Bankers Trust Company.

PAUL J. JASINSKI,  PRESIDENT,  TREASURER AND CHIEF FINANCIAL OFFICEr,  2/17/47,
Managing Director, Investors Bank & Trust Company, 1990 - present.

TIMOTHY J.  COYNE,  VICE  PRESIDENT,  5/9/67,  Director,  Corporate  Marketing,
Investors  Bank & Trust  Company,  1997 - present,  Vice  President,  Corporate
Sales,  Dreyfus  Corporation,  1995 - 1997,  Assistant Vice President,  Concord
Financial Corp., 1992 - 1995.

CHRISTOPHER  J. QUINN,  ASSISTANT VICE  PRESIDENT,  5/6/66,  Manager,  Advisory
Client  Services,  Investors  Bank & Trust  Company,  1996 -  present,  Service
Specialist  Mutual Funds,  Fleet Bank, 1994 - 1996,  Executive Sales Assistant,
Concord Financial Corp., 1993 - 1994.



SUSAN C. MOSHER,  SECRETARY,  1/29/55,  Director,  Mutual Fund Administration -
Legal Administration, Investors Bank & Trust Company, 1995 - present.

SANDRA I. MADDEN, ASSISTANT SECRETARY,  8/29/66, Associate Counsel, Mutual Fund
Administration - Legal  Administration,  Investors Bank & Trust Company, 1999 -
present;  Associate Counsel at Scudder Kemper  Investments,  Inc. in the Mutual
Fund Administration Group of the Legal Department, 1996-1999.

COMPENSATION OF THE TRUSTEES AND OFFICERS.  Neither the Trust nor the Portfolio
Trust compensates the Trustees or officers of the Trust and the Portfolio Trust
who are affiliated with Investors Bank. None of the Trustees or officers of the
Trust or the Portfolio  Trust have engaged in any financial  transactions  with
the Trust or the Portfolio  Trust,  respectively,  during the fiscal year ended
December 31, 1999.

The  Trustees of the  Portfolio  Trust are paid an annual  retainer of $10,000,
payable in equal  quarterly  installments,  and a $2,500  meeting  fee for each
quarterly meeting attended. The Trustees of the Trust are paid a $1,000 meeting
fee for each  quarterly  meeting  attended.  The following  table  reflects the
compensation  paid by the Trust,  by the Portfolio Trust and by another related
open-end investment company, to each Trustee for the fiscal year ended December
31, 1999.


                                     B - 7

<PAGE>

                   Aggregate        Pension or Retirement    Total Compensation
                   Compensation     Benefits Accrued as      From Trust and Fund
Name of Trustee    From the Trust   Part of Portfolio's      Complex *
- ---------------    --------------   -------------------      ------------------
                                    Expenses
                                    ---------

Kevin J. Sheehan        $0                  $0                       $0

Francis J. Gaul, Jr.    $20,000             $0                       $26,250

Edward F. Hines, Jr.    $20,000             $0                       $26,250

Thomas E. Sinton        $20,000             $0                       $26,250

*Fund Complex  consists of the Trust,  the Portfolio Trust, the Merrimac Global
Cash Fund and the Merrimac  Series,  comprising eight series as of December 31,
1999.



ITEM 14.    CONTROL PERSONS AND PRINCIPAL HOLDERS OF SECURITIES



Control is defined by the 1940 Act as the beneficial ownership, either directly
or through  one or more  controlled  companies,  of more than 25 percent of the
voting securities of the company.

As of April 3, 2000,  the  Merrimac  Cash Fund (the "Cash  Fund")  beneficially
owned  approximately  65.9% of the outstanding  interests of the Cash Portfolio
and the Merrimac  Cash Series  beneficially  owned  approximately  32.9% of the
outstanding interests of the Cash Portfolio,  each were,  therefore,  deemed as
control  persons  of the Cash  Portfolio.  As of April 3,  2000,  the  Merrimac
Treasury Series,  a series of Merrimac  Series,  owned 100% of the value of the
outstanding  shares of the Treasury  Portfolio,  and, therefore was deemed as a
control  person of the Treasury  Portfolio.  As of April 3, 2000,  the Merrimac
Treasury Plus Series, a series of Merrimac  Series,  owned 100% of the value of
the  outstanding  shares of the Treasury  Plus  Portfolio,  and,  therefore was
deemed as a control person of the Treasury Plus Portfolio. As of April 3, 2000,
the Merrimac U.S. Government Series, a series of Merrimac Series, owned 100% of
the value of the  outstanding  shares of the U.S.  Government  Portfolio,  and,
therefore was deemed as a control person of the U.S. Government Portfolio.

As of April 3, 2000,  Trustees and officers of the Trust owned in the aggregate
less than 1% of any of the
Portfolios.



ITEM 15.    INVESTMENT ADVISORY AND OTHER SERVICES

INVESTMENT ADVISER AND SUBADVISERS



Each Portfolio retains Investors Bank & Trust Company  ("Investors Bank" or the
"Adviser") as their investment adviser.  The Investment Adviser Agreements (the
"Adviser  Agreements")  between Investors Bank and each Portfolio provides that
Investors  Bank will manage the  operations of each  Portfolio,  subject to the
policies established by the Board of Trustees of the Trust. Investors Bank also
provides  office  space,  facilities,  equipment  and  personnel  necessary  to
supervise each  Portfolio's  operations and pays the  compensation of each such
Portfolio's officers, employees and directors who are affiliated with Investors
Bank.  Each  Portfolio  pays  Investors  Bank a  unitary  fee for  services  as
Investment  Adviser,  Administrator,  Custodian,  Fund  Accountant and Transfer
Agent.  For a description of the rate of compensation  that each Portfolio pays
Investors Bank under the Adviser Agreements, see "Administrator, Transfer Agent
and Fund Accountant" below.

The fees earned by Investors  Bank from the Cash Portfolio for the fiscal years
ended  December  31,  1997,

                                     B - 8

<PAGE>

December 31, 1998 and December 31, 1999 were  $2,314,064 of which  $381,468 was
waived, $1,760,305 of which $384,213 was waived, and $2,117,982,  respectively.
The fees earned by Investors  Bank from the Treasury  Portfolio  for the fiscal
years ended  December  31,  1997,  December 31, 1998 and December 31, 1999 were
$1,932,596,  $98,068 and $302,524,  respectively.  The fees earned by Investors
Bank from the Treasury Plus Portfolio for the period beginning January 22, 1999
(commencement  of  operations)  to December  31, 1999 were  $397,835.  The fees
earned by  Investors  Bank from the U.S.  Government  Portfolio  for the period
beginning June 29, 1999  (commencement of operations) to December 31, 1999 were
$123,332.

Pursuant  to  an  Investment   Sub-Adviser   Agreement  (the  "AAM  Sub-Adviser
Agreement"),  Investors  Bank has retained  Allmerica  Asset  Management,  Inc.
("AAM") as sub-adviser to the Cash Portfolio and the U.S. Government Portfolio.
AAM is  compensated  by  Investors  Bank  at no  additional  cost  to the  Cash
Portfolio and the U.S.  Government  Portfolio.  Subject to the  supervision  of
Investors Bank and of the Portfolio Trust's Board of Trustees, AAM furnishes to
the Cash  Portfolio  and the U.S.  Government  Portfolio  investment  research,
advice and supervision  and determines what securities will be purchased,  held
or  sold by the  Cash  Portfolio  and the  U.S.  Government  Portfolio.  AAM is
rendered an annual fee,  computed  and paid  monthly,  based on the average net
assets ("ANA") of each of the Cash Portfolio and the U.S. Government  Portfolio
according to the following schedule: 0.09% on the first $500 million in assets;
0.07% on the next $500  million in  assets,  and 0.06% on assets  exceeding  $1
billion. Prior to September 1, 1998, the Cash Portfolio was advised by The Bank
of New York ("BNY") and BNY was paid an annual fee,  computed and paid monthly,
based on 0.08% of the ANA of the Cash  Portfolio.  The amount paid by Investors
Bank to BNY for the period January 1, 1998 to August 31, 1998 was $429,014. The
amount  paid by  Investors  Bank to AAM for the  period  September  1,  1998 to
December 31, 1998 was $233,588 and for the fiscal year ended  December 31, 1999
was $997,094.  The amount paid by Investors  Bank to AAM as  sub-adviser to the
U.S.  Governemnt  Portfolio  for the  period  June 29,  1999  (commencement  of
operations) to December 31, 1999 was $65,311.

Pursuant  to  an  Investment   Sub-Adviser   Agreement  (the  "M&I  Sub-Adviser
Agreement"),  Investors  Bank has  retained  M&I  Investment  Management  Corp.
("M&I")  as  sub-adviser  to the  Treasury  Portfolio  and  the  Treasury  Plus
Portfolio.  M&I is compensated  by Investors Bank at no additional  cost to the
Treasury Portfolio and the Treasury Plus Portfolio.  Subject to the supervision
of Investors Bank and of the Portfolio Trust's Board of Trustees, M&I furnishes
to the Treasury Portfolio and the Treasury Plus Portfolio  investment research,
advice and supervision  and determines what securities will be purchased,  held
or sold by Treasury  Portfolio  and Treasury Plus  Portfolio.  Until January 4,
1999, the Treasury Portfolio was advised by Aeltus Investment Management,  Inc.
("Aeltus")  and Aeltus  received the same fees as M&I currently  receives.  The
amount  accrued and paid by Investors  Bank to Aeltus for the fiscal year ended
December  31,  1998 was  $46,158  and for 1999 was  $755.  The  amount  paid by
Investors Bank to M&I as  sub-adviser to the Treasury  Portfolio for the fiscal
year ended December 31, 1999 was $145,788. The amount paid by Investors Bank to
M&I as  sub-adviser  to the Treasury Plus  Portfolio for the period January 22,
1999 (commencement of operations) to December 31, 1999 was $183,100.

Each Portfolio  bears the expenses of its operations  other than those incurred
by AAM or M&I,  respectively.  Among the other  expenses,  each  Portfolio pays
share pricing and shareholder  servicing fees and expenses;  custodian fees and
expenses;  legal  and  auditing  fees and  expenses;  expenses  of  shareholder
reports;  registration  and  reporting  fees and  expenses;  and the  Portfolio
Trust's Trustee fees and expenses.



ADMINISTRATOR, TRANSFER AGENT, CUSTODIAN AND FUND ACCOUNTANT

IBT Trust & Custodial Services (Ireland) LMTD ("IBT Ireland"),  a subsidiary of
Investors Bank & Trust Company ("Investors  Bank"),  serves as Administrator to
the  Portfolios.   The  services   provided  by  IBT  Ireland  include  certain
accounting,  clerical and bookkeeping services,  corporate secretarial services
and

                                     B - 9

<PAGE>

assistance in the preparation of reports to shareholders.

IBT Fund Services (Canada) Inc., ("IBT Canada") a subsidiary of Investors Bank,
serves as transfer and dividend  paying agent for the  Portfolios.  As transfer
agent, IBT Canada is responsible for maintaining records of holders in interest
and for the payment of distributions for each Portfolio.

Investors  Bank  also  acts as  custodian  for the  Portfolios.  As  custodian,
Investors  Bank holds cash,  securities  and other assets of the  Portfolios as
required by the 1940 Act. IBT Canada also serves as fund  accounting  agent for
the  Portfolios.   As  fund  accounting  agent,  IBT  Canada  performs  certain
accounting, clerical and bookkeeping services, and the daily calculation of net
asset value for each Portfolio.

INDEPENDENT AUDITORS



For the fiscal year ended  December 31, 1999,  Ernst & Young LLP ("E&Y") served
as  independent  auditors  to  the  Portfolio  Trust.  E&Y is  responsible  for
performing annual audits of the financial  statements and financial  highlights
in accordance with generally accepted accounting standards,  and preparation of
the Federal tax returns. Additionally,  pursuant to Rule 17f-2 of the 1940 Act,
three  security  counts are  performed  for the  Portfolio  Trust.  The mailing
address for E&Y is 200 Clarendon Street, Boston, Massachusetts 02116.



COUNSEL

Goodwin, Procter & Hoar LLP serves as counsel to the Portfolio Trust.

ITEM 16.   BROKERAGE ALLOCATION AND OTHER PRACTICES

Purchases  and sales of  securities  for the  Portfolios  usually are principal
transactions.  Securities  are normally  purchased  directly from the issuer or
from an  underwriter or market maker for the  securities.  There usually are no
brokerage  commissions  paid  for  such  purchases.  Each  Portfolio  does  not
anticipate  paying  brokerage  commissions.   Any  transaction  for  which  the
Portfolios  pay a brokerage  commission  will be effected at the best price and
execution  available.  Purchases  from  underwriters  of  securities  include a
commission or concession  paid by the issuer to the  underwriter  and purchases
from dealers  serving as market makers  include the spread  between the bid and
asked price.

Allocations of transactions,  including their frequency,  to various dealers is
determined  by the  respective  Sub-Advisers  in their best  judgment  and in a
manner  deemed  to be in the  best  interest  of the  other  investors  in each
Portfolio  rather  than by any  formula.  The primary  consideration  is prompt
execution of orders in an effective manner at the most favorable price.

Investment  decisions for the Portfolios will be made  independently from those
for any other account or investment company that is or may in the future become
managed by the  Sub-Advisers.  If,  however,  each Portfolio and other accounts
managed by its  Sub-Adviser  are  contemporaneously  engaged in the purchase or
sale of the same  security,  the  transactions  may be averaged as to price and
allocated equitably to each account. In some cases, this policy might adversely
affect the price paid or received by each Portfolio or the size of the position
obtainable for each Portfolio. In addition, when purchases or sales of the same
security for each Portfolio and for other accounts managed by their Sub-Adviser
occur contemporaneously, the purchase or sale orders may be aggregated in order
to obtain any price  advantages  available to large  denomination  purchases or
sales.

                                    B - 10

<PAGE>

ITEM 17.    CAPITAL STOCK AND OTHER SECURITIES

Under the Declaration of Trust,  interests in each Portfolio have no preemptive
or  conversion  rights,  and are fully paid and  non-assessable,  except as set
forth in the Prospectus. The Portfolio Trust normally will not hold meetings of
holders of such interests  except as required under the 1940 Act. The Portfolio
Trust  would be  required to hold a meeting of holders in the event that at any
time less than a majority of its  Trustees  holding  office had been elected by
holders.  The  Trustees of the  Portfolio  Trust  continue to hold office until
their  successors are elected and have  qualified.  Holders holding a specified
percentage  of interests  in a Portfolio  may call a meeting of holders in such
Portfolio  for the purpose of removing any Trustee.  A Trustee of the Portfolio
Trust may be removed upon a majority vote of the  interests  held by holders in
the Portfolio  Trust  qualified to vote in the election.  The 1940 Act requires
the  Portfolio  Trust to assist its  holders in  calling  such a meeting.  Upon
liquidation of a Portfolio,  holders in a Portfolio  would be entitled to share
pro rata in the net  assets of the  Portfolio  available  for  distribution  to
holders.  Each holder in a Portfolio is entitled to a vote in proportion to its
percentage interest in such Portfolio.


ITEM 18.   PURCHASE, REDEMPTION AND VALUATION OF SHARES

MANNER IN WHICH SHARES ARE OFFERED

An investment in a Portfolio may be made without a sales load. All  investments
are made at net asset value next  determined  after an order is received by the
Portfolio.  The net asset value of a Portfolio is  determined  on each Business
Day.  Securities  are  valued at  amortized  cost,  which the  Trustees  of the
Portfolios  have  determined  in good  faith  constitutes  fair  value  for the
purposes of complying with the 1940 Act. This valuation method will continue to
be used until such time as the  Trustees of the  Portfolios  determine  that it
does not constitute fair value for such purposes.

VALUATION OF SHARES
The investment securities in each Portfolio are valued based upon the amortized
cost  method  which  involves  valuing a  security  at its cost and  thereafter
assuming a constant  amortization  to  maturity  of any  discount  or  premium.
Although the amortized cost method  provides  consistency in valuation,  it may
result in  periods  during  which the stated  value of a security  is higher or
lower than the price that each  Portfolio  would  receive if the security  were
sold.

ITEM 19.   TAXATION OF THE TRUST

Each Portfolio is treated as a partnership for federal income tax purposes.  As
such, a Portfolio is not subject to federal  income  taxation.  Each  Portfolio
will  allocate  at  least  annually  among  its  investors,   each   investor's
distributive  share of the  Portfolio's  net  investment  income,  net realized
capital gains, and any other items of income, gain, loss, deduction or credit.

If a Portfolio invests in zero coupon  securities,  certain  increasing rate or
deferred interest securities or, in general,  other securities with an original
issue discount (or with market  discount if an election is in effect to include
market discount in income currently),  the Portfolio must accrue income on such
investments prior to the receipt of the corresponding cash payments.

ITEM 21.   CALCULATION OF PERFORMANCE DATA

Not applicable.

                                    B - 11

<PAGE>

ITEM 22.    FINANCIAL STATEMENTS



The Portfolios' financial statements contained in the 1999 Annual Report of the
Trust have been  audited by Ernst & Young LLP,  independent  auditors,  and are
incorporated  by  reference  into this SAI.  Copies of the Trust's  1999 Annual
Report may be obtained by calling 1-888-MERRMAC.



                                    B - 12

<PAGE>

                                   APPENDIX

DESCRIPTION OF COMMERCIAL PAPER RATINGS

The following  descriptions  of short-term  debt ratings have been published by
Standard & Poor's  Ratings  Service  ("Standard & Poor's"),  Moody's  Investors
Service  ("Moody's"),  Fitch's IBCA Investors Service  ("Fitch"),  and Duff and
Phelps ("Duff"),  respectively. These obligations have an original maturity not
exceeding thirteen months, unless explicitly noted.

A -- Standard & Poor's  commercial paper rating is a current  assessment of the
likelihood  of timely  payment of debt  considered  short-term  in the relevant
market.  Commercial  paper issues rated A-1 by Standard & Poor's reflect a very
strong degree of safety of timely  payment.  Commercial  paper issues rated A-2
reflect a strong  degree of safety of timely  payment  but not as strong as for
issues designated A-1.

Commercial paper issues rated Prime-1 by Moody's are judged by Moody's to be of
the  "highest"  quality  on the basis of  relative  repayment  capacity  with a
superior  ability  for  repayment  of  senior   short-term  debt   obligations.
Commercial  paper  issues  rated  Prime-2  are  judged by  Moody's to be of the
"second  highest"  quality  with a  strong  ability  for  repayment  of  senior
short-term debt obligations.

The rating Fitch-1 (Highest Grade) is the highest commercial rating assigned by
Fitch.  Paper  rated  Fitch-1 is  regarded  as having the  strongest  degree of
assurance  for timely  payment.  Commercial  paper  issues  rated  Fitch-2  are
regarded as having only a slightly less  assurance of timely payment than those
issues rated Fitch-1.

The rating  Duff-1 is the highest  commercial  paper  rating  assigned by Duff.
Paper rated Duff-1 is regarded as having very high  certainty of timely payment
with excellent  liquidity factors that are supported by ample asset protection.
Risk factors are minor.  The rating Duff-2 is regarded as having good certainty
of  timely  payment  with  sound  liquidity  factors  supported  by good  asset
protection. Risk factors are small.

DESCRIPTION OF LONG-TERM DEBT RATINGS

The following is a description of Moody's debt instrument ratings:

Aaa -- Bonds  which are rated Aaa are  judged to be of the best  quality.  They
carry the smallest degree of investment  risk and are generally  referred to as
"gilt edged". Interest payments are protected by a large or by an exceptionally
stable margin and principal is secure.  While the various  protective  elements
are likely to change,  such changes as can be  visualized  are most unlikely to
impair the fundamentally strong position of such issues.

Aa --  Bonds  which  are  rated  Aa are  judged  to be of high  quality  by all
standards.  Together with the Aaa group they comprise what are generally  known
as high-grade  bonds.  They are rated lower than the best bonds because margins
of  protection  may not be as  large as in Aaa  securities  or  fluctuation  of
protective  elements may be of greater amplitude or there may be other elements
present  which make the  long-term  risk  appear  somewhat  larger than the Aaa
securities.

Moody's  applies  numerical  modifiers  1,  2  and  3 in  each  generic  rating
classification.  The  modifier 1  indicates  that the  obligation  ranks in the
higher end of its generic rating category;  the modifier 2 indicates

                                    B - 13

<PAGE>

a midrange ranking;  and the modifier 3 indicates a ranking in the lower end of
that generic rating category.

The following is a description of Standard & Poor's debt instrument ratings:

Standard & Poor's  ratings  are based,  in varying  degrees,  on the  following
considerations:  (i) the  likelihood of default -- capacity and  willingness of
the obligor as to the timely  payment of interest and repayment of principal in
accordance with the terms of the obligations; (ii) the nature of and provisions
of the obligation;  and (iii) the protection afforded by, and relative position
of,  the  obligation  in the  event  of  bankruptcy,  reorganization,  or other
arrangement  under the laws of bankruptcy and other laws  affecting  creditors'
rights.

AAA -- Debt rated AAA has the  highest  rating  assigned  by Standard & Poor's.
Capacity to pay interest and repay principal is extremely strong.

AA -- Debt  rated AA has a very  strong  capacity  to pay  interest  and  repay
principal and differs from the highest rated issues only in small degree.

Plus (+) or minus (-): The ratings may be modified by the addition of a plus or
minus sign to show relative standing within the major rating categories.

THOMSON BANK WATCH SHORT-TERM DEBT RATINGS

Thomson Bank Watch  ratings  represent an  assessment  of the  likelihood of an
untimely  payment  of  principal  and  interest.  Important  factors  that  may
influence this  assessment are the overall  financial  health of the particular
company,  and the  probability  that the  government  will come to the aid of a
troubled institution in order to avoid a default or failure. The probability of
government intervention stems from four primary factors:

o  Government Guarantees

o  Government Or Quasi-Government Ownership Or Control

o  The Degree Of Concentration In The Banking System

o  Government Precedent

As with the Issuer  Ratings,  the  Short-Term  Debt  Ratings  incorporate  both
qualitative  and  quantitative  factors.  The  ratings  are  not  meant  to  be
"pass/fail"  but rather to provide a relative  indication of  creditworthiness.
Therefore, obligations rated TBW-3 are still considered investment-grade.

These  Short-Term  Debt  Ratings  can  also be  restricted  to  local  currency
instruments.  In such cases, the ratings will be preceded by the designation LC
for Local  Currency.  Short-Term  Debt Ratings are based on the following scale
and the definitions are:

TBW-1                                                                     LC-1
       The highest  category;  indicates a very high  likelihood that principal
       and interest will be paid on a timely basis.

                                     B - 14

<PAGE>

TBW-2                                                                     LC-2
       The second-highest category; while the degree of safety regarding timely
       repayment of principal  and interest is strong,  the relative  degree of
       safety is not as high as for issues rated TBW-1.

TBW-3                                                                     LC-3
       The  lowest   investment-grade   category;   indicates  that  while  the
       obligation is more  susceptible to adverse  developments  (both internal
       and external)  than those with higher  ratings,  the capacity to service
       principal and interest in a timely fashion is considered adequate.

TBW-4                                                                     LC-4
       The lowest rating  category;  this rating is regarded as  non-investment
       grade and therefore speculative.

THOMSON BANK WATCH LONG-TERM DEBT RATINGS

Long-Term  Debt  Ratings  assigned  by THOMSON  BANK  WATCH ALSO WEIGH  HEAVILY
GOVERNMENT  OWNERSHIP AND SUPPORT. The quality of both the company's management
and  franchise  are of even greater  importance  in the  Long-Term  Debt Rating
decisions.  Long-Term  Debt  Ratings look out over a cycle and are not adjusted
frequently for what is believed to be short-term performance aberrations.

Long-Term  Debt Ratings can be restricted to local currency debt - ratings will
be identified by the  designation  LC. In addition,  Long-Term Debt Ratings may
include a plus (+) or minus (-) to indicate where within the category the issue
is placed. Thomson Bank Watch Long-Term Debt Ratings are based on the following
scale:

INVESTMENT GRADE

AAA                                                                     LC-AAA
       Indicates  that the ability to repay  principal and interest on a timely
       basis is extremely high.

AA                                                                       LC-AA
       Indicates a very strong  ability to repay  principal  and  interest on a
       timely basis,  within limited  incremental risk compared to issues rated
       in the highest category.

A                                                                         LC-A
       Indicates the ability to repay principal and interest is strong.  Issues
       rated A could be more vulnerable to adverse  developments (both internal
       and external) than obligations with higher ratings.

BBB                                                                     LC-BBB
       The lowest investment-grade  category;  indicates an acceptable capacity
       to repay  principal  and  interest.  BBB issues are more  vulnerable  to
       adverse  developments (both internal and external) than obligations with
       higher ratings.

                                    B - 15

<PAGE>

NON-INVESTMENT GRADE - MAY BE SPECULATIVE IN THE LIKELIHOOD OF TIMELY REPAYMENT
OF PRINCIPAL AND INTEREST.

BB                                                                       LC-BB
       While not investment  grade,  the BB rating suggests that the likelihood
       of default is considerably  less than for lower-rated  issues.  However,
       there are  significant  uncertainties  that could  affect the ability to
       adequately service debt obligations.

B                                                                         LC-B
       Issues rated B show a higher degree of uncertainty and therefore greater
       likelihood of default than  higher-rated  issues.  Adverse  developments
       could  negatively  affect the payment of  interest  and  principal  on a
       timely basis.

CCC                                                                     LC-CCC
       Issues rated CCC clearly have a high likelihood of default,  with little
       capacity to address further adverse changes in financial circumstances.

CC                                                                       LC-CC
       CC is applied to issues that are subordinate to other  obligations rated
       CCC and are  afforded  less  protection  in the event of  bankruptcy  or
       reorganization.

D                                                                         LC-D
       Default









                                    B - 16

<PAGE>





                                    PART C

Item 23.  Exhibits

             Exhibit No.        Description
             -----------        -----------

             (a1)       Declaration of Trust, effective as of October 30,
                        1996(1)

             (a2)       Amendment No. 1 to the Declaration of Trust (2)

             (a3)       Amendment No. 2 to the Declaration of Trust(3)

             (a4)       Amendment No. 3 to the Declaration of Trust(3)

             (b)        By-Laws(1)

             (c)        None

             (d1)       Investment Adviser Agreement between the Registrant
                        and Investors Bank & Trust Company ("Investors  Bank")
                        (Cash Portfolio)(1)

             (d2)       Investment Adviser Agreement between the Registrant
                        and Investors Bank (Treasury Portfolio)(3)

             (d3)       Investment Adviser Agreement between the Registrant and
                        Investors Bank (Treasury Plus Portfolio)(3)



             (d4)       Investment Adviser Agreement between the Registrant and
                        Investors Bank (U.S. Government Portfolio)(4)



             (d5)       Investment Sub-Adviser Agreement between Investors Bank
                        and Allmerica Asset Management, Inc. ("AAM")(Cash
                        Portfolio)(3)

             (d6)       Investment Sub-Adviser Agreement between Investors Bank
                        and M&I Investment Management Corp. ("M&I")(Treasury
                        Portfolio)(3)

             (d7)       Investment Sub-Adviser Agreement between Investors Bank
                        and M&I (Treasury Plus Portfolio)(3)



             (d8)       Investment Sub-Adviser Agreement between Investors Bank
                        and AAM (U.S. Government Portfolio)(4)



                                     C - 1

<PAGE>

             (e)        *

             (f)        Not Applicable

             (g)        Custodian Agreement between Registrant and Investors
                        Bank(1)

             (h1)       Fund Accounting Agreement between Registrant and IBT
                        Fund Services (Canada) Inc.(1)

             (h2)       Administration Agreement between Registrant and IBT
                        Trust & Custodial Services (Ireland) Limited (1)

             (h3)       Transfer Agency Agreement between Registrant and IBT
                        Trust & Custodial Services (Ireland) Limited (1)

             (i)        *

             (j)        *

             (k)        *

             (l)        None

             (m)        Not Applicable

             (o)        Not Applicable

(1)  Incorporated by reference to the  Registrant's  Registration  Statement on
Form N-1A filed March 28, 1997 (Accession No. 0001029869-97-000386).

(2)  Incorporated by reference to the  Registrant's  Registration  Statement on
Form N-1A filed April 21, 1998 (Accession No. 0001029869-98-000530).



(3)  Incorporated by reference to the Registrant's Registration Statement on
Form N-1A filed April 28, 1999 (Accession No. 0000897436-99-000105).

(4)  Filed herein.



*Pursuant to General  Instructions  B2 of Form N-1A, a  registration  statement
filed under only the Investment Company Act of 1940 shall consist of the facing
sheet of the Form, responses to all items of Part A and B except Items 1, 2, 3,
5 and 9 of Part A thereof,  responses to all items of Part C except Items 23(e)
and  (i)-(k)  and the  required  signatures  and all other  documents  that are
required  or  which  the  Registrant  may  file  as  part  of the  registration
statement.

                                     C - 2

<PAGE>

Item 24. Persons Controlled by or Under Common Control with Registrant



As of the close of  business  on April 3, 2000,  the  following  entities  were
deemed control persons of the respective Portfolio.

Control is defined by the 1940 Act as the beneficial ownership, either directly
or through  one or more  controlled  companies,  of more than 25 percent of the
voting securities of the company.

Record Owner                                            Percent Ownership
- ------------                                            -----------------
Merrimac Cash Fund                                           65.9%
Merrimac Cash Series                                         32.9%

Record Owner                                            Percent Ownership
- ------------                                            -----------------
Merrimac Treasury Series                                     100%

Record Owner                                            Percent Ownership
- ------------                                            -----------------
Merrimac Treasury Plus Series                                100%

Record Owner                                            Percent Ownership
- ------------                                            -----------------
Merrimac U.S. Government Series                              100%



Item 25. Indemnification

Under  Article V of the  Registrant's  Declaration  of Trust,  the Trust  shall
indemnify,  to the fullest  extent  permitted by law  (including the 1940 Act),
each Trustee, officer or employee of the Trust (including any Person who serves
at  the  Trust's  request  as  a  director,   officer  or  trustee  of  another
organization in which the Trust has any interest as a shareholder,  creditor or
otherwise)  against all  liabilities  and expenses  (including  amounts paid in
satisfaction  of  judgments,  in  compromise,  as fines and  penalties,  and as
counsel fees) reasonably incurred by such Person in connection with the defense
or  disposition  of any  action,  suit or other  proceeding,  whether  civil or
criminal, in which such Person may be involved or with which such Person may be
threatened,  while in office or  thereafter,  by reason of such Person being or
having  been such a Trustee,  officer,  employee,  except  with  respect to any
matter as to which such Person shall have been  adjudicated  to have acted with
bad faith, willful misfeasance,  gross negligence or reckless disregard of such
Person's duties,  such  liabilities and expenses being  liabilities only of the
Portfolio Series out of which such claim for indemnification arises;  provided,
however,  that as to any matter  disposed  of by a  compromise  payment by such
Person,  pursuant to a consent decree or otherwise,  no indemnification  either
for such payment of for any other expenses  shall be provided  unless there has
been a  determination  that such Person did not engage in willful  misfeasance,
bad faith, gross negligence or reckless disregard of the duties involved in the
conduct of such  Person's  office (i) by the court or other body  approving the
settlement  or  other  disposition;  or (ii)  based  upon a review  of  readily
available facts (as opposed to a full trial-type  inquiry),  by written opinion
from independent legal counsel approved by the Trustees; or (iii) by a majority
of the Trustees who are neither  Interested Persons of the Trust nor parties to
the  matter,  based upon a review of readily  available  facts (as opposed to a
full trial-type inquiry).

Item 26. Business and Other Connections of Investment Adviser

Investors Bank serves as investment  adviser to the Registrant.  Investors Bank
was organized in 1969 as a  Massachusetts-chartered  trust company and provides
domestic and global custody, multi-currency accounting,  institutional transfer
agency,  performance  measurement,  foreign  exchange,  securities  lending and
mutual fund  administration  services to a variety of financial asset managers,
including  mutual fund  complexes,  investment  advisers,  banks and  insurance
companies.  The business,  profession,  vocation or employment of a substantial
nature that each  director or officer of

                                     C - 3

<PAGE>

Investors  Bank is or has been,  at any time during the past two fiscal  years,
engaged  in for  his own  account  or in the  capacity  of  director,  officer,
employee, partner or trustee, is as follows:

                                                       Business and Other
                                                       Positions Within
Name                 Position With Adviser             Last Two Years
- ----                 ---------------------             --------------

Kevin J. Sheehan     President & Chief Executive       Chief Executive Officer
                     Officer                           since June 1995;
                                                       President since June
                                                       1992

Michael F. Rogers    Executive Vice President          since September 1993

Karen C. Keenan      Senior Vice President, Chief      Treasurer since
                     Financial Officer and Treasurer   September 1997; Senior
                                                       Vice President and Chief
                                                       Financial Officer since
                                                       June 1995

Edmund J. Maroney    Senior Vice President,            since July 1991
                     Technology

Robert D. Mancuso    Senior Vice President,            since September 1993
                     Marketing Client Services

David F. Flynn       Senior Vice President-Lending     since April 1992

John E. Henry        General Counsel & Secretary       since January 1997;
                                                       General Counsel &
                                                       Assistant Secretary
                                                       since February 1996

James M. Oates       Director                          Chairman of IBEX Capital
                                                       Markets, LLC since 1996.

Thomas P. McDermott  Director                          Managing Director of TPM
                                                       Associates since 1994.

Frank B. Condon      Director                          Chief Executive Officer
                                                       & Chairman of The
                                                       Woodstock Corporation
                                                       from 1993 to April 1997.

                                     C - 4

<PAGE>

Phyllis S. Swersky   Director                          President of The Meltech
                                                       Group since 1995;
                                                       President & Chief
                                                       Executive Officer of The
                                                       NET Collaborative from
                                                       1996 to 1997.

Donald G. Friedl     Director                          President of All Seasons
                                                       from 1986 until January
                                                       1997.

Robert B. Fraser     Director                          Retired, Formerly,
                                                       Chairman of Goodwin,
                                                       Procter & Hoar, L.L.P.

Item 27. Principal Underwriters

Not Applicable

Item 28. Location of Accounts and Records

The accounts and records of the Registrant are located, in whole or in part, at
the office of the Registrant and the following locations:

Investors Bank & Trust Company
200 Clarendon  Street
Boston, MA 02116
(Investment Adviser and Custodian)

Allmerica Asset Management, Inc.
440 Lincoln Street
Worcester, MA  01653
(Investment Sub-Adviser)

M&I Investment Management Corp.
1000 North Water Street
Milwaukee, Wisconsin 53202
(Investment Sub-Adviser)

IBT Trust & Custodial Services (Ireland) LMTD
Deloitte & Touche House
29 Earlsfort Terrace
Dublin 2, Ireland
(Administrator)

                                     C - 5

<PAGE>

IBT Fund Services (Canada) Inc.
1 First Canadian, King Street West
Suite 2800 P.O. Box 231
Toronto, CA  M5X1C8
(Transfer Agent and Fund Accountant)

Item 29. Management Services

Not Applicable

Item 30. Undertakings

Not Applicable.






















                                     C - 6

<PAGE>





                                  SIGNATURES

Pursuant to the requirements of the Investment Company Act of 1940, as amended,
the  Registrant  has duly  caused  this  Amendment  No.  3 to the  Registration
Statement on Form N-1A to be signed on its behalf by the  undersigned,  thereto
duly authorized in the City of Boston and the  Commonwealth of Massachusetts as
of the 28th day of April, 2000.

                                MERRIMAC MASTER PORTFOLIO

                                    /s/ Paul J. Jasinski
                                    ---------------------

                                    Paul J. Jasinski
                                    President













<PAGE>





                                 Exhibit Index

        Exhibit No.         Description
        -------------------------------

         (d4)            Investment Adviser Agreement between the
                         Registrant and Investors Bank (U.S. Government
                         Portfolio)

         (d8)            Investment Sub-Adviser Agreement between
                         Investors Bank and AAM (U.S. Government Portfolio)








                         INVESTMENT ADVISER AGREEMENT



     Agreement made as of this 2nd day of June,  1999, by and between  Merrimac
Master  Portfolio,  a New York Trust (the "Trust") and Investors Bank and Trust
Company (the "Adviser"), a Massachusetts banking corporation.

     WHEREAS,  the MERRIMAC U.S.  GOVERNMENT  PORTFOLIO (the  "Portfolio") is a
series of the Trust,  which is an open-end  diversified  management  investment
company  registered as such with the  Securities and Exchange  Commission  (the
"SEC")  pursuant to the  Investment  Company Act of 1940, as amended (the "1940
Act");

     WHEREAS,  the Merrimac U.S.  Government  Series (the "Fund"),  which is an
open-end diversified  management investment company registered as such with the
SEC pursuant to the 1940 Act and the Securities Act of 1933, will invest all of
its investable assets in the Portfolio;

     WHEREAS,  the Trust,  on behalf of the  Portfolio,  desires to appoint the
Adviser to render,  or contract to obtain as hereinafter  provided,  investment
advisory services to the Portfolio and to administer the Portfolio's day to day
business  affairs and the 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,  the Trust,  on behalf of the Portfolio,  and the
Adviser,  the parties  hereto,  intending to be legally bound,  hereby agree as
follows:

1.  Appointment

     (a) The Trust, on behalf of the Portfolio,  hereby appoints the Adviser as
the investment  adviser of the Portfolio to administer its business affairs and
to perform for the Portfolio such other duties and functions as are hereinafter
set forth.  The Adviser hereby accepts such  appointment and agrees to give the
Portfolio and the Trust's Board of Trustees  (the  "Trustees"),  the benefit of
the Adviser's best judgment,  effort,  advice and recommendations in respect of
its duties as defined in Section 2.

     (b) The  Trust  hereby  represents  and  warrants  to the  Adviser,  which
representations  and warranties  shall be deemed to be continuing,  that (i) it
has full  power and  authority  to enter into this  Agreement,  and (ii) it has
taken all  necessary  and proper action to authorize the execution and delivery
of this Agreement.

     (c) The  Adviser  hereby  represents  and  warrants  to the  Trust,  which
representations  and warranties  shall be deemed to be continuing,  that (i) it
has full  power and  authority  to enter into this  Agreement,  and (ii) it has
taken all  necessary  and proper action to authorize the execution and delivery
of this Agreement.

2.  Adviser Duties

     (a) The  Adviser  shall,  subject  to the  direction  and  control  of the
Trustees and in accordance with the objective and policies of the Portfolio and
the implementation  thereof as set forth in the Fund's Prospectus and Statement
of Additional  Information ("SAI"), the Portfolio's  Registration  Statement on
Form N-1A and any federal  and state laws:  (i)  regularly  provide  investment
advice and  recommendations  to the Portfolio,  with respect to the Portfolio's
investments,  investment policies and the purchase and sale of securities; (ii)
supervise and monitor  continuously the investment program of the Portfolio and
the  composition  of its  portfolio  and  determine  what  securities  shall be
purchased and sold by the Portfolio; (iii) arrange, subject to the provision of
Section 4 hereof,  for the purchase of securities and other investments for the
Portfolio and the sale of securities  and other  investments  of the Portfolio;
(iv) provide reports on the

                                       1

<PAGE>

foregoing  to the Trust in such detail as the Trust may  reasonably  deem to be
appropriate  in order to permit the Trust to  determine  the  adherence  by the
Adviser to the investment policies and legal requirements of the Portfolio; and
(v) make its  officers  and  employees  available  to the  Trust's  officers at
reasonable  times to review the  investment  policies of the  Portfolio  and to
consult  with the Trust's  officers  regarding  the  investment  affairs of the
Portfolio.

     (b)  The  Adviser  is  further  authorized  to  enter  into a  sub-adviser
arrangement for the investment  advisory  services outlined in Section 2 (a) of
this Agreement in connection  with the  management of the  Portfolio,  provided
that no such arrangement  shall be made until a sub-adviser  agreement has been
approved  by the  Trustees.  Should the Adviser  enter into such a  sub-adviser
agreement, the Adviser shall,  nevertheless,  retain supervisory responsibility
for  all  investment   advisory  services   furnished   pursuant  to  any  such
sub-advisory  arrangements  and the Adviser's  duties shall then  include:  (i)
supervise and monitor  continuously the investment  advisory services furnished
pursuant to any such sub-adviser  arrangements;  (ii) review the performance of
the sub-adviser,  and make  recommendations to the Trustees with respect to the
retention and renewal of such sub-adviser  arrangements;  (iii) provide reports
on the foregoing to the Trustees for each Board meeting; (iv) make its officers
and employees  available to review the investment policies of the Portfolio and
to  consult  with the  sub-adviser  regarding  the  investment  affairs  of the
Portfolio;  (v) supervise relationships with and monitor the performance of the
custodian, depositories,  transfer agent, accountants,  attorneys, insurers and
other  persons in any capacity  deemed to be necessary or  desirable;  and (vi)
make  recommendations  to the Trustees  with respect to Portfolio  policies and
carry out such policies as are adopted by the Trustees.

3. Compensation of the Adviser

     The Portfolio  will pay to the Adviser as  compensation  for the Adviser's
services  rendered  and  for  the  expenses  borne  by the  Adviser,  including
personnel  expenses,  a fee,  determined  as  described  in Schedule A which is
attached hereto and made a part hereof.

4.  Portfolio Transactions and Brokerage

     The Adviser  shall place all orders for the purchase and sale of portfolio
securities  for the  Portfolio's  account  with  issuers,  brokers  or  dealers
selected by the Adviser,  which may include  where  permissible  under the 1940
Act, brokers or dealers  affiliated with the Adviser.  In the selection of such
brokers or dealers and the placing of such  orders,  the Adviser  always  shall
seek best  execution,  which is to place  transactions  where the Portfolio can
obtain  the most  favorable  combination  of price and  execution  services  in
particular  transactions  or  provided  on a  continuing  basis by a broker  or
dealer,  and to deal  directly  with a  principal  market  in  connection  with
over-the-counter  transactions,  except when it is believed that best execution
is obtainable elsewhere.

5.  Interested Trustees or Parties

     It is understood that Trustees,  officers,  and  shareholders of the Trust
may be or become interested in the Adviser as directors,  officers or employees
and that directors,  officers and  stockholders of the Adviser may be or become
similarly  interested  in the  Trust,  and that the  Adviser  may be or  become
interested in the Trust as a shareholder or otherwise.

6.  Services Not Exclusive

     The  services  of  the  Adviser  to the  Portfolio  are  not to be  deemed
exclusive,  the Adviser  being free to render  services to others and engage in
other activities, provided, however, that such other services and activities do
not, during the term of this Agreement,  interfere,  in a material manner, with
the Adviser's ability to meet all of its obligations hereunder.

                                       2

<PAGE>

7.  Compliance; Books and Records

     (a) The  Adviser  agrees to maintain  adequate  compliance  procedures  to
ensure its compliance  with the  applicable  provisions of the 1940 Act and any
rules  or  regulations  thereunder,  the  investment  objective,  policies  and
restrictions  of the Portfolio as set forth in the current Fund  Prospectus and
SAI and any other applicable provisions of state or federal law.

     (b)  The  Adviser  shall  furnish  to the  Portfolio,  at the  Portfolio's
expense,  copies of all records  prepared in connection with the performance of
this Agreement and the  maintenance of compliance  procedures  pursuant to this
Section 7 as the Portfolio may reasonably request.

     (c)  The  Adviser  agrees  to  provide  upon  reasonable  request  of  the
Portfolio,  information  regarding  the Adviser,  including but not limited to,
background  information  about  the  Adviser  and  its  personnel,  for  use in
connection with efforts to promote the Fund and the sale of its shares.

     (d) In compliance with the  requirements of Rule 31a-3 under the 1940 Act,
the Adviser hereby agrees that all records which it maintains for the Trust are
the property of the Trust and further agrees to surrender promptly to the Trust
any of such records upon the Trust's  request.  The Adviser  further  agrees to
preserve  for the  periods  prescribed  by Rule  31a-2  under  the 1940 Act the
records required to be maintained by Rule 31a-1 under the 1940 Act. The Adviser
will  treat  confidentially  and as  proprietary  information  of the Trust all
records  and other  information  relative  to the Fund and  prior,  present  or
potential shareholders, except as otherwise required by law.

8.  Limitation of Liability of Adviser

     In  consideration  of the  Adviser's  undertaking  to render the  services
described in this Agreement, the Trust, on behalf of the Portfolio, agrees that
the Adviser  shall not be liable under this  Agreement for any loss suffered by
the Trust in connection with the  performance of this Agreement,  provided that
nothing in this Agreement  shall be deemed to protect or purport to protect the
Adviser  against any  liability to the Trust or its  shareholders  to which the
Adviser would otherwise be subject by reason of willful misfeasance,  bad faith
or negligence in the performance of its duties under this Agreement.

9.  Duration, Amendment and Termination

     (a) Subject to prior  termination as provided in  sub-section  (d) of this
Section 9, this  Agreement  shall  continue in effect  until two years from the
date hereof and for successive annual periods  thereafter,  but only so long as
the  continuance  after such  initial  two year  period  shall be  specifically
approved at least  annually by vote of the Trustees or by vote of a majority of
the outstanding voting securities of the Portfolio and the Fund.

     (b) This Agreement may be modified by the written Agreement of the Adviser
and the  Portfolio,  such consent on the part of the Portfolio to be authorized
by vote of a majority of the outstanding voting securities of the Portfolio and
the  Fund if  required  by law.  The  execution  of any  such  modification  or
amendment  by a party shall  constitute  a  representation  and warranty to the
other party that all  necessary  consents  or  approvals  with  respect to such
modification or amendment have been obtained.

     (c) In addition to the  requirements of  sub-sections  (a) and (b) of this
Section 9, the terms of any  continuance or  modification of the Agreement must
have been  approved  by the vote of a majority  of those  Trustees  who are not
parties to such  Agreement  or  interested  persons of any such party,  cast in
person at a meeting called for the purpose of voting on such approval.

     (d) Either the  Adviser or the  Portfolio  may,  at any time on sixty (60)
days'  prior  written  notice to the other  party,  terminate  this  Agreement,
without payment of any penalty, and in the case of the Portfolio,  by action of
its Trustees, or by vote of a majority of its outstanding voting securities.

                                       3

<PAGE>

     (e) This  Agreement  shall  terminate  automatically  in the  event of its
assignment.

     (f)  Termination of this  Agreement  shall not relieve the Adviser nor the
Trust from any liability or obligation in respect of any matters,  undertakings
or conditions  which shall not have been done,  observed or performed  prior to
such termination. All records of the Portfolio in the possession of the Adviser
shall be returned to the Portfolio as soon as reasonably  practicable after the
termination of this Agreement.

10.  Disclaimer of Liability; Several Obligations

     The  Adviser  understands  that the  obligations  of the Trust  under this
Agreement  are not  binding  upon  any  Trustee  or  shareholder  of the  Trust
personally, but bind only the Trust and the Trust's property.

     This  Agreement is an  agreement  entered into between the Adviser and the
Trust on behalf of the  Portfolio.  With respect to any obligation of the Trust
on behalf of any other  Portfolio  arising out of this  Agreement,  the Adviser
shall look for payment or satisfaction of such obligation  solely to the assets
of the  Portfolio  to which such  obligation  relates as though the Adviser had
separately  contracted  with the  Trust by  separate  written  instrument  with
respect to each Portfolio.

11.  Miscellaneous

     (a) The terms "vote of a majority of the outstanding  voting  securities,"
"assignment,"  and  "interested  persons,"  when used  herein,  shall  have the
respective  meanings specified in the 1940 Act as now in effect or as hereafter
amended.

     (b) The  captions  in this  Agreement  are  included  for  convenience  of
reference only and in no way define or delimit any of the provisions  hereof or
otherwise affect their construction or effect.

     (c) If any provision of this Agreement  shall be held or made invalid by a
court  decision,  statute,  rule or otherwise,  the remainder of this Agreement
shall not be affected thereby.

     (d) This  Agreement  shall be binding upon and shall insure to the benefit
of the parties hereto and their respective successors.

     (e) The Adviser's duties and  responsibilities  are solely those set forth
herein and no other covenant or obligation shall be implied against the Adviser
in connection with this Agreement.

     (f) This  Agreement  may be  executed in two or more  counterparts,  which
taken together shall constitute one and the same instrument.

     (g) Any notice under this  Agreement  shall be in writing,  addressed  and
delivered  or mailed,  postage  prepaid,  to the other party at such address as
such other party may designate for the receipt of such notice.  No notice shall
be effective until received.

     IN WITNESS WHEREOF, the parties have caused this instrument to be executed
by their  respective  officers  designated  below as of the day and year  first
above written.




                                       4

<PAGE>

                        Merrimac Master Portfolio ("TRUST") on behalf of
                        the Merrimac U.S. Government Portfolio ("PORTFOLIO")

                        By:      /s/ Paul J. Jasinski
                            ------------------------------
                                 Paul J. Jasinski

                        Title: President
                               ---------



                        INVESTORS BANK & TRUST COMPANY
                        ("ADVISER")

                        By:      /s/ Robert Mancuso
                            ------------------------------
                                 Robert Mancuso

                        Title: Senior Vice President
                               ---------------------
















                                       5




                       INVESTMENT SUB-ADVISER AGREEMENT


Agreement  made as of this 2nd day of June,  1999,  between  Investors Bank and
Trust  Company  (the  "Adviser"),  a  Massachusetts  banking  corporation,  and
Allmerica  Asset  Management,   Inc.  (the   "Sub-Adviser"),   a  Massachusetts
corporation.

WHEREAS,  MERRIMAC U.S.  GOVERNMENT  PORTFOLIO (the "Portfolio") is a series of
the Merrimac Master Portfolio (the "Trust"),  which is an open-end  diversified
management  investment  company  registered  as such  with the  Securities  and
Exchange Commission (the "SEC") pursuant to the Investment Company Act of 1940,
as amended (the "1940  Act"),  and the Trust has  appointed  the Adviser as the
investment  adviser for the  Portfolio,  pursuant to the terms of an Investment
Adviser Agreement (the "Adviser Agreement"); and

WHEREAS,  the  Merrimac  U.S.  Government  Series (the  "Series"),  an open-end
diversified  management  investment  company  registered  as such  with the SEC
pursuant to the 1940 Act and the  Securities Act of 1933, as amended (the "1933
Act") will invest all of its investable assets in the Portfolio; and

WHEREAS,  the Adviser  Agreement  provides that the Adviser may, at its option,
subject to approval by the Trustees of the Trust and, to the extent  necessary,
shareholders  of  the  Portfolio,  appoint  a  sub-adviser  to  assume  certain
responsibilities  and  obligations of the Adviser under the Adviser  Agreement;
and

WHEREAS,  the Adviser desires to appoint the Sub-Adviser as its sub-adviser for
the Portfolio and the  Sub-Adviser  is willing to act in such capacity upon the
terms herein set forth; and

NOW THEREFORE,  in  consideration  of the premises and of the mutual  covenants
herein  contained,  the  Adviser  and  the  Sub-Adviser,  the  parties  hereto,
intending to be legally bound, hereby agree as follows:

1.  Appointment
- ---------------

          (a) The Adviser  hereby  appoints the  Sub-Adviser  as the investment
          sub-adviser  of the  Portfolio  to provide  investment  advice and to
          perform for the  Portfolio  such other  duties and  functions  as are
          hereinafter   set  forth.   The   Sub-Adviser   hereby  accepts  such
          appointment and agrees to give the Portfolio and the Trust's Board of
          Trustees  (the  "Trustees"),  directly  or through the  Adviser,  the
          benefit  of the  Sub-Adviser's  best  judgment,  effort,  advice  and
          recommendations in respect of its duties as defined in Section 2.

          (b) The Adviser hereby  represents  and warrants to the  Sub-Adviser,
          which   representations   and  warranties   shall  be  deemed  to  be
          continuing,  that (i) it has full power and  authority  to enter into
          this Agreement and to delegate  investment  management  discretion on
          behalf of the Portfolio to the Sub-Adviser, and (ii) it has taken all
          necessary  and proper  action to authorize the execution and delivery
          of this Agreement.

          (c) The  Sub-Adviser  hereby  represents and warrants to the Adviser,
          which   representations   and  warranties   shall  be  deemed  to  be
          continuing,  that (i) it has full power and  authority  to enter into
          this Agreement, and (ii) it has taken all necessary and proper action
          to authorize the execution and delivery of this Agreement.

                                       1

<PAGE>

2.  Delivery of Documents
- -------------------------

Prior  to the  execution  of this  Agreement,  the  Adviser  will  furnish  the
Sub-Adviser with copies,  properly  certified or authenticated,  of each of the
following documents:

          (a) The Trust's Agreement and Declaration; and all amendments thereto
          or restatements thereof;

          (b) The Trust's By-Laws; and all amendments thereto;

          (c)  Resolutions  of the Trust's  Board of Trustees  authorizing  the
          appointment of the Sub-Adviser and approving this Agreement;

          (d) The Trust's  original  Notification  of Registration on Form N-8A
          under the 1940 Act;

          (e) The Trust's initial Registration Statement on Form N-1A under the
          1940 Act and all amendments thereto;

          (f) The current  Prospectus  or similar  document of any entity which
          the Trust has authorized as an investor (the  "Authorized  Investor")
          in the Portfolio (the "Investor Offering Documents");

          (g) The  policies  and  procedures  applicable  to the  Portfolio  as
          adopted by the Trustees; and all amendments and supplements thereto.

          (h)  Any  further  documents,   materials  or  information  that  the
          Sub-Adviser may reasonably  request from time to time to enable it to
          perform its duties pursuant to this Agreement.

3.  Sub-Adviser Duties
- ----------------------

The Sub-Adviser shall,  subject to the direction and control of the Trustees or
the Adviser, and in accordance with the objective and policies of the Portfolio
and the implementation thereof as set forth in the Investor Offering Documents,
the Portfolio's  Registration Statement on Form N-1A and any applicable federal
and state laws: (i) regularly provide investment advice and  recommendations to
the Portfolio, with respect to the Portfolio's investments, investment policies
and  the  purchase  and  sale  of   securities;   (ii)  supervise  and  monitor
continuously the investment program of the Portfolio and the composition of its
portfolio  and  determine  what  securities  shall be purchased and sold by the
Portfolio;  (iii) arrange,  subject to the provisions of Section 5 hereof,  for
the purchase of securities and other investments for the Portfolio and the sale
of securities and other  investments of the Portfolio;  (iv) provide reports on
the foregoing to the Adviser in such detail as the Adviser may reasonably  deem
to be  appropriate in order to permit the Adviser to determine the adherence by
the  Sub-Adviser  to the  investment  policies  and legal  requirements  of the
Portfolio;  and (v) make its officers and employees available to the Adviser at
reasonable  times to review the  investment  policies of the  Portfolio  and to
consult with the Adviser regarding the investment affairs of the Portfolio.

4.  Compensation of the Sub-Adviser
- -----------------------------------

The Adviser will pay to the Sub-Adviser as compensation  for the  Sub-Adviser's
services  rendered  and for  the  expenses  borne  by the  Sub-Adviser,  a fee,
determined as described in Schedule A which is attached  hereto and made a part
hereof.  Such fee  shall be paid by the  Adviser  and the Trust  shall  have no
liability

                                       2

<PAGE>

therefor.  Nothing in this  Agreement  shall  require the  Sub-Adviser  to bear
expenses of the Adviser, the Portfolio or the Trust.

5.  Portfolio Transactions and Brokerage
- ----------------------------------------

The  Sub-Adviser  shall place all orders for the purchase and sale of portfolio
securities  for the  Portfolio's  account  with  issuers,  brokers  or  dealers
selected by the Sub-Adviser, which may include where permissible under the 1940
Act, brokers or dealers  affiliated with the  Sub-Adviser.  In the selection of
such  brokers or dealers and the  placing of such  orders,  the Adviser  always
shall seek best execution,  which is to place  transactions where the Portfolio
can obtain the most favorable  combination  of price and execution  services in
particular  transactions  or  provided  on a  continuing  basis by a broker  or
dealer,  and to deal  directly  with a  principal  market  in  connection  with
over-the-counter  transactions,  except when it is believed that best execution
is obtainable elsewhere. Nothing in this Agreement shall preclude the combining
of orders for the sale or  purchase of  securities  or other  investments  with
other accounts managed by the Sub-Adviser or its affiliates,  provided that the
Sub-Adviser does not favor any account over any other account and provided that
any purchase or sale orders executed contemporaneously shall be allocated in an
equitable manner among the accounts involved.

6.  Interested Trustees or Parties
- ----------------------------------

It is understood that Trustees,  officers, and shareholders of the Trust may be
or become  interested in the Adviser or the Sub-Adviser as directors,  officers
or employees and that  directors,  officers and  stockholders of the Adviser or
the Sub-Adviser may be or become  similarly  interested in the Trust,  and that
the Adviser or the  Sub-Adviser  may be or become  interested in the Trust as a
shareholder or otherwise.

7.  Services Not Exclusive
- --------------------------

The services of the Sub-Adviser to the Adviser are not to be deemed  exclusive,
the  Sub-Adviser  being free to render  services  to others and engage in other
activities,  provided, however, that such other services and activities do not,
during the term of this Agreement,  interfere,  in a material manner,  with the
Sub-Adviser's  ability to meet all of its obligations with respect to rendering
investment  advice  hereunder.  The  Sub-Adviser,  its affiliates and its other
clients may at any time acquire or dispose of securities  which are at the same
time being  acquired  or  disposed  of for the  account of the  Portfolio.  The
Sub-Adviser shall not be obligated to acquire for the Portfolio any security or
other investment which the Sub-Adviser or its affiliates may acquire for its or
their own accounts or for the account of another client.

8.  Compliance;  Books and Records
- ----------------------------------

          (a) The Sub-Adviser  agrees to maintain  compliance  procedures which
          are reasonably designed to ensure the Portfolio's compliance with the
          applicable  provisions  of the 1940 Act and any rules or  regulations
          thereunder and the investment objective, policies and restrictions of
          the  Portfolio  as  set  forth  in  the  current  Investor   Offering
          Documents.

          (b) The  Sub-Adviser  shall furnish to the Adviser,  at the Adviser's
          expense,  copies of all records prepared and maintained in connection
          with  the  performance  of  this  Agreement  and the  maintenance  of
          compliance  procedures  pursuant to this Section 8 as the Adviser may
          reasonably request.

                                       3

<PAGE>

          (c) The Sub-Adviser  agrees to provide upon reasonable request of the
          Adviser,  information  regarding the  Sub-Adviser,  including but not
          limited to,  background  information  about the  Sub-Adviser  and its
          personnel and performance data, for use in connection with efforts to
          promote the Fund and the sale of its shares.

          (d) In compliance with the  requirements of Rule 31a-3 under the 1940
          Act,  the  Sub-Adviser  hereby  agrees  that  all  records  which  it
          maintains  for the Trust are the  property  of the Trust and  further
          agrees to  surrender  promptly to the Trust any of such  records upon
          the Trust's request.  The Sub-Adviser  further agrees to preserve for
          the periods  prescribed  by Rule 31a-2 under the 1940 Act any records
          which it is  required  to  maintain by Rule 31a-1 under the 1940 Act.
          The  Sub-Adviser  will  treat   confidentially   and  as  proprietary
          information of the Trust all records and other  information  obtained
          from the Trust  relative  to the  Authorized  Investors  and prior or
          potential shareholders, except as otherwise required by law.

9.  Limitation of Liability of Sub-Adviser; Indemnification
- -----------------------------------------------------------

In  consideration  of the  Sub-Adviser's  undertaking  to render  the  services
described in this Agreement,  the Adviser agrees that the Sub-Adviser shall not
be liable for any loss  suffered  by the  Adviser,  the Trust,  the  Authorized
Investors  or their  shareholders,  or the  Portfolio  in  connection  with the
performance of this Agreement, provided that nothing in this Agreement shall be
deemed to protect or purport to protect the  Sub-Adviser  against any liability
to the Adviser, the Trust, the Authorized  Investors or their shareholders,  or
the Portfolio to which the Sub-Adviser  would otherwise be subject by reason of
willful  misfeasance,  bad faith or negligence in the performance of its duties
under this Agreement.

10.  Duration, Amendment and Termination
- ----------------------------------------

          (a) Subject to prior  termination as provided in  sub-section  (d) of
          this Section 10, this  Agreement  shall  continue in effect until two
          years  from  the  date  hereof  and  for  successive  annual  periods
          thereafter,  but only so long as the  continuance  after such initial
          two year period shall be  specifically  approved at least annually by
          vote  of the  Board  of  Trustees  or by vote  of a  majority  of the
          outstanding  voting  securities of the  Portfolio and the  Authorized
          Investors.

          (b) This  Agreement  may be modified by the written  agreement of the
          Adviser, the Sub-Adviser and the Portfolio,  such consent on the part
          of the  Portfolio  to be  authorized  by  vote of a  majority  of the
          outstanding  voting  securities of the  Portfolio and the  Authorized
          Investors if required by law. The execution of any such  modification
          or  amendment  by a  party  shall  constitute  a  representation  and
          warranty  to  the  other  parties  that  all  necessary  consents  or
          approvals  with respect to such  modification  or amendment have been
          obtained.

          (c) In addition to the  requirements of  sub-sections  (a) and (b) of
          this  Section  10,  the  terms of any  continuance,  modification  or
          amendment of the  Agreement  must have been approved by the vote of a
          majority of those  Trustees who are not parties to such  Agreement or
          interested  persons  of any such  party,  cast in person at a meeting
          called for the purpose of voting on such approval.

          (d) Either the Adviser,  the Sub-Adviser or the Portfolio may, at any
          time on sixty (60) days' prior written  notice to the other  parties,
          terminate this Agreement,  without payment of any penalty, and in the
          case of the Portfolio, by action of its Board of Trustees, or by vote
          of a majority of its outstanding voting securities.

                                       4

<PAGE>

          (e) This Agreement shall terminate  automatically in the event of its
          assignment.

          (f)  Termination of this Agreement  shall not relieve the Adviser nor
          the  Sub-Adviser  from any  liability or obligation in respect of any
          matters,  undertakings or conditions  which shall not have been done,
          observed or performed prior to such  termination.  All records of the
          Portfolio in the possession of the  Sub-Adviser  shall be returned to
          the Portfolio as soon as reasonably practicable after the termination
          of this Agreement.

11.  Disclaimer of Shareholder Liability
- ----------------------------------------

The Adviser and the  Sub-Adviser  understand  that the obligations of the Trust
under this  Agreement  are not binding upon any Trustee or  shareholder  of the
Trust personally, but bind only the Trust and the Trust's property.

12.  Miscellaneous
- ------------------

          (a)  The  terms  "vote  of  a  majority  of  the  outstanding  voting
          securities,"   "assignment,"  and  "interested  persons,"  when  used
          herein,  shall have the respective meanings specified in the 1940 Act
          as now in effect or as hereafter amended.

          (b) The captions in this  Agreement are included for  convenience  of
          reference  only and in no way define or delimit any of the provisions
          hereof or otherwise affect their construction or effect.

          (c) If any provision of this Agreement  shall be held or made invalid
          by a court  decision,  statute,  rule or otherwise,  the remainder of
          this Agreement shall not be affected thereby.

          (d) This  Agreement  shall be  binding  upon and  shall  inure to the
          benefit of the parties hereto and their respective successors.

          (e) This Agreement may be executed in two or more counterparts, which
          taken together shall constitute one and the same instrument.

          (f) Any notice under this  Agreement  shall be in writing,  addressed
          and delivered or mailed,  postage prepaid, to the other party at such
          address as such other  party may  designate  for the  receipt of such
          notice. No notice shall be effective until received.








                                       5

<PAGE>

     IN WITNESS WHEREOF, the parties have caused this instrument to be executed
by their  respective  officers  designated  below as of the day and year  first
above written.



                              INVESTORS BANK & TRUST COMPANY ("ADVISER")


                              By: /s/Kevin J. Sheehan
                                  ----------------------------------
                              Name:  Kevin J. Sheehan
                              Title: President



                              ALLMERICA ASSET MANAGEMENT, INC. ("SUB-ADVISER")


                              By: /s/John P. Kavanaugh
                                  -----------------------------------
                              Name:  John P. Kavanaugh
                              Title: President



The Merrimac Master Portfolio on behalf of the
Merrimac U.S. Government Portfolio hereby acknowledges
the execution of this Agreement

Merrimac Master Portfolio
("THE TRUST")


By: /s/Paul J. Jasinski
    ----------------------------------
Name:  Paul J. Jasinski
Title: President











                                       6

<PAGE>

                                  SCHEDULE A

The  Adviser  will  pay  to  the  Sub-Adviser  as  full  compensation  for  the
Sub-Adviser's services rendered an annual fee, computed and paid monthly, based
on the average daily net assets of the Portfolio  according to the schedule set
forth below.  The fee for each month shall be payable  within 30 business  days
after the end of the month.

If the  Sub-Adviser  shall  serve for any period  less than a full  month,  the
foregoing compensation shall be prorated according to the proportion which such
period bears to a full month.

                  0.09% on the first $500,000,000 in assets;
                 0.07% on the next $500,000,000 in assets; and
                   0.06% on assets exceeding $1,000,000,000




















                                       7



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