....another way to do it would be conditional formatting. In the second cell
from the top, go to "Format" then "Conditional Formatting". Change the drop
down from "Cell is" to "Formula is" then type =A2=A1 and choose a format
(highlight yellow or something). Then copy A2 and Paste Special...Formats
as far down the page as you need to. You can then occasionally sort you
serial numbers and duplicates will highlight yellow.

"PeterM" wrote:

First of all a happy happy Holiday greetings from a grateful reader here.
You guys are the best.....I'm wondering if it is possible, if Excel can
notify me if I enter a duplicate number into a cell. I need to enter serial
numbers of inventory, and sometimes I get my sheets mixed up, and enter the
same info again. Can that be avoided??????