You should have told us what the condition is.

This will allow only No in B1 if the logical test is TRUE. If the logical
test is FALSE then it will allow only Yes or No.

=IF(logical_test,B1="No",OR(B1="Yes",B1="No"))

--
Biff
Microsoft Excel MVP


"Bob Myers" wrote in message
...
I'm looking for a custom formula for data validation in a cell. The user
is to be allowed to enter either Yes or No in accordance with the
following logic:

If (True, "No", Or("Yes", "No")) {If a condition is True, he can't do
it; otherwise, he has a choice.}

Respectfully submitted,
Bob Myers