Use Data Validation in the 2nd row down, with a type of Custom and a formula
of

=COUNTIF($A$1:A1,A2)=0

--
HTH

Bob Phillips

(replace somewhere in email address with gmail if mailing direct)

"ShamsulZ" wrote in message
...
I'm looking for formula that enable excel to prompt when the data that i'm
written is already typed. e.g cont no. abcd1234567 will be prompted by
excel
when i'm typing the no again. Thanks friend!