<PAGE>
ALLMERICA INVESTMENT TRUST
(SUPPLEMENT TO PROSPECTUS AND STATEMENT OF ADDITIONAL
INFORMATION DATED MAY 1, 1999)
Effective April 1, 2000, TCW Investment Management Company ("TCW") will replace
Cambiar Investors, Inc. ("Cambiar") as Sub-Adviser of the Select Strategic
Growth Fund (the "Fund") of Allmerica Investment Trust (the "Trust").
TCW, a wholly-owned subsidiary of The TCW Group, Inc., a Nevada corporation, is
located at 865 South Figueroa Street, Suite 1800, Los Angeles, CA 90017. TCW is
a member of a group of companies which, as of December 31, 1999, had
approximately $70 billion in assets under management or committed to management.
Christopher J. Ainley, Douglas S. Foreman and Charles Larsen will have
responsibility for the day-to-day management of the Fund's investments. Mr.
Ainley, a Managing Director, joined TCW in 1994. Prior to joining TCW, Mr.
Ainley spent two years at Putnam Investments as a Vice President and Analyst in
the Equity Research Group and then as a Portfolio Manager for the Core Equity
Group. Mr. Foreman, Group Managing Director and Chief Investment Officer - U.S.
Equities and a Chartered Financial Analyst, joined TCW in 1994. Prior to joining
TCW, Mr. Foreman was employed by Putnam Investments where he spent his last five
years managing institutional accounts and mutual funds. Mr. Larsen, Managing
Director, and a Chartered Financial Analyst and Chartered Investment Counselor,
joined TCW in 1984. Prior to joining TCW, Mr. Larsen was a Senior Vice President
and Portfolio Manager for CIGNA Investment Management Company.
At a meeting on February 15, 2000, the Board of Trustees of the Trust approved a
Sub-Adviser Agreement (the "New Sub-Adviser Agreement") between Allmerica
Financial Investment Management Services, Inc., the investment manager of the
Trust (the "Manager"), and TCW. Under the New Sub-Adviser Agreement, the Manager
will pay TCW a fee computed daily and paid quarterly at an annual rate of 0.85%
based on the average daily net assets of the Fund of up to $100 million. When
the average daily net assets of the Fund exceed $100 million, TCW will receive a
fee computed daily and paid quarterly at an annual rate of 0.75% of the total
average daily net assets of the Fund. Under the current Sub-Adviser Agreement
with Cambiar (the "Current Sub-Adviser Agreement"), the Manager pays Cambiar a
fee computed daily and paid quarterly at an annual rate of the average daily net
assets of the Fund as set forth below:
Net Assets Fee
---------- ---
First $50 Million.................. 0.50%
Next $100 Million.................. 0.45%
Next $100 Million.................. 0.35%
Next $100 Million.................. 0.30%
Over $350 Million.................. 0.25%
The other terms of the New Sub-Adviser Agreement are substantially the same as
those of the Current Sub-Adviser Agreement. Since the Manager is responsible for
the payment of all sub-adviser fees, the level of sub-adviser fees has no impact
on the operating expenses of the Fund. There is no change in the investment
management fee paid by the Fund to the Manager.
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In addition, effective April 1, 2000, the Fund's current investment objective,
principal investment strategies and principal risks will be replaced with the
following:
Investment Objective: The Fund seeks long-term capital appreciation.
Principal Investment Strategies: To pursue its investment objective, the Fund
invests (except when maintaining a temporary defensive position) at least 65% of
the value of its total assets in equity securities issued by companies with
market capitalization, at the time of acquisition by the Fund, within the
capitalization range of the companies comprising the Standard & Poor's Small Cap
600 Index.
In managing the Fund's investments, the Sub-Adviser pursues a small cap growth
investment philosophy. The Sub-Adviser uses fundamental company-by-company
analysis in conjunction with technical and quantitative market analysis to
screen potential investments and to continuously monitor securities in the
Fund's portfolio.
The Fund focuses on small, fast-growing companies that offer cutting-edge
products, services or technologies. Because these companies are often in their
early stages of development, their stocks tend to fluctuate more than most other
securities. The Fund may invest up to 25% of its assets in foreign securities
(not including its investments in American Depositary Receipts).
Principal Risks:
. Company Risk
. Currency Risk
. Derivatives Risk
. Foreign Investment Risk
. Investment Management Risk
. Liquidity Risk
. Market Risk
---------------------
The section relating to the Growth Fund in the table containing information
about the individuals who are primarily responsible for the day-to-day
management of the Funds under "Management of the Funds" in the Trust's
Prospectus is amended to delete Nicholas Kovich and add the following
individuals:
<TABLE>
<CAPTION>
Fund Name and Name and Title of Service with Business Experience
Sub-Adviser Name Portfolio Manager(s) Sub-Adviser for Past Five Years
- ---------------- -------------------- ----------- -------------------
<S> <C> <C> <C>
Growth Fund Chris Leavy, 1997 - Present Prior to joining MAS, Mr.
Miller Anderson & Sherrerd, LLP CFA and Vice President Leavy was employed by
("MAS") Capitoline Investment Services
as a portfolio Manager from
1995-1997.
</TABLE>
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<TABLE>
<CAPTION>
Fund Name and Name and Title of Service with Business Experience
Sub-Adviser Name Portfolio Manager(s) Sub-Adviser for Past Five Years
- ---------------- -------------------- ----------- -------------------
<S> <C> <C> <C>
Steven Epstein, 1996-Present Prior to joining MAS, Mr.
Vice President Epstein attended the Wharton
School, University of Pennsylvania from
1994-1996, receiving an MBA.
Eric F. Scharpf, 1997 - Present Prior to joining MAS, Mr.
Vice President Scharpf attended the Wharton
School, University of Pennsylvania from
1995-1997 receiving an MBA, and served as
a Financial Analyst for Salomon Brothers
from 1993-1995.
The section relating to the Investment Grade Income Fund in the same table noted above is amended to read as follows:
Investment Grade Income Fund Ann K. Tripp, 1987 - Present She joined AAM in 1987 and
Allmerica Asset Management, Inc. Vice President has served as a Vice President
("AAM") of the firm since 1993.
</TABLE>
Dated: March 7, 2000
