<PAGE>
Allmerica Investment Trust
(Supplement Effective September 1, 1999 to Prospectus dated May 1, 1999)
The information relating to the Select Aggressive Growth Fund and the Select
Capital Appreciation 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)***
Select Capital Appreciation Fund None 0.94%*** None 0.10% 1.04%(1),(2)***
</TABLE>
*** Effective September 1, 1999, the management fee rates for the Select
Aggressive Growth Fund and Select Capital Appreciation Fund were revised.
The Management Fee and Total Annual Fund Operating Expense ratios shown in
the table above have been adjusted to assume that the revised rates took
effect on January 1, 1998.
The percentages shown in footnote (2) under the heading, "Fees and Expenses of
the Funds", in the section entitled, "Expense Summary", in the Prospectus are
changed to 0.86% for the Select Aggressive Growth Fund and 1.02% for the Select
Capital Appreciation Fund.
The information relating to the Select Aggressive Growth Fund and the Select
Capital Appreciation 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
Select Capital Appreciation Fund $104 $325 $563 $1,246
