Thanks Jim. It works fine.
.....considering that "aa" limits the user to enter just the letters 'aa',
what should be the input mask should I need to allow any alphabetic
character, that is, a-z?

cheers

"Jim Rech" wrote:

You might try this validation formula, where the validation cell is A1:

=AND(LEN(A1)=7,LEFT(A1,2)="aa",RIGHT(A1,1)="a",VAL UE(MID(A1,3,4)))

--
Jim
"archiboy" wrote in message
...
| when entering data in a cell, i need to restrict users to enter the
following
| alphanumeric combination and nothing more.
|
| "aa####a", where "a" is an alphabetic character (a-z) and "#" is a number
| (0-9)
|
| i cannot figure out the formula to use under the 'custom' section of
Data -
| Validation
|
| pls help! thanks