<PAGE>
Allmerica Investment Trust
(Supplement Effective September 1, 1999 to Prospectus dated May 1, 1999)
The information relating to the Select Aggressive Growth Fund in the table 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>
Select Aggressive Growth Fund None 0.82% *** None 0.07% 0.89% (1),(2)***
</TABLE>
*** Effective September 1, 1999, the management fee rate for the Select
Aggressive Growth Fund was revised. The Management Fee and Total Annual
Fund Operating Expense ratios shown in the table above have been adjusted
to assume that the revised rate took effect on January 1, 1998.
The percentage shown in footnote (2) under the heading, "Fees and Expenses of
the Funds", in the section entitled, "Expense Summary", in the Prospectus is
changed to 0.86% for the Select Aggressive Growth Fund.
The information relating to the Select Aggressive Growth Fund in the table under
the heading, "Example", in the section entitled, "Expense Summary", in the
Prospectus is amended as follows:
1 Year 3 Years 5 Years 10 Years
------ ------- ------- --------
Select Aggressive Growth Fund $89 $278 $483 $1,074
