Use a custom validation (under "allow") and input this formula (under
"formula").

=ISERROR(FIND(UPPER(A1),A1))=FALSE

"Simon Jefford" wrote:

Is it possible to ensure that only capital letters are entered into a cell.

I have tried using a list within data-validation but the cell still allows
both upper and lower case entries.

Any ideas would be much appreciated.
Thanks
Simon