<PAGE>
ALLMERICA INVESTMENT TRUST (THE "TRUST")
(SUPPLEMENT EFFECTIVE AUGUST 21, 2000 TO PROSPECTUS DATED MAY 1, 2000)
Effective October 1, 2000, the information relating to the Money Market Fund in
the tables under the heading, "Fees and Expenses of the Funds", in the section
entitled, "Expense Summary", in the Prospectus is amended as follows:
<TABLE>
<CAPTION>
Shareholder Annual Fund Operating Expenses Total Annual
Fees (expenses deducted from Fund assets) Fund
(fees paid directly Management Distribution Other Operating
from your investment) Fees (12b-1) Fees Expenses Expenses
--------------------- ----------- ------------- -------- ------------
<S> <C> <C> <C> <C> <C>
Money Market Fund None 0.31%** None 0.05% 0.36%(1)**
</TABLE>
** Effective October 1, 2000, the management fee rate for the Money Market
Fund has been revised. The expense information in the table has been restated
to reflect current fees.
The information relating to the Money Market Fund in the table under the
heading, "Example", in the section entitled, "Expense Summary", in the
Prospectus is amended as follows:
<TABLE>
<CAPTION>
1 Year 3 Years 5 Years 10 Years
------ ------- ------- --------
<S> <C> <C> <C> <C>
Money Market Fund $37 $116 $202 $456
</TABLE>
