Select the column, in this example, column A.

Select Data | Validation... | Settings tab | Allow: Custom and put the
folowing formula in the Formula box:

=COUNTIF($A:$A,$A1)<2

You will now not be able to create a duplicat entry in column A

Regards

Trevor


"Selina" wrote in message
...
Am attempting to set up database in Excel and need to format one column so
that it does not accept duplicate entries through the column?