Using Find with Grep

[Rick Weinbender <lsrwein@central-ph.k12.mo.us>]

How can I make the following expression
display only occurrences that do NOT contain the
searchstring.  Is this possible?

find /home -name *.txt -exec grep searchstring {} \;

I want to search for the absense of a particular commandline
in a user config file.

TIA,

-Rick