Select the column (say it's Col D), use Data/Validation, change Allow Any
Value to Allow Custom, enter =COUNTIF(D:D,D1)=1, then choose an appropriate
error message on the error tab if you wish. This won't change any already
existing duplicates, but you can find those by tools/auditing/show auditing
toolbar, then click the "circle Invalid Data" toorbar button (looks like a
gridline with red circles)

"Mike" wrote:

Hi

I have a column of text and I need to be alerted if the same text appears
more than twice in the column. The column changes on a regular basis. e.g.

Tom
Tom
Jane
Mary
Tom

"ALERT AN ITEM APPEARS MORE THAN TWICE"

Thanks Mike