functions and grants question

In other databases, stored procedures run under the privilege of the 
stored procedure owner.  Is it supposed to work the same in postgresql?

I am the owner of the database, tables and functions.  When I grant 
execute permission on a function to another user, that user gets 
permission denied errors on the tables the stored procedure is 
accessing.  Any idea what I may be doing wrong?

Thanks,
Avi
-- 
Avi Schwartz
avi@CFFtechnologies.com