Using data validation you can; but only manual entries/dropdown entries will
be validated

--Select A1:J10
--Select menu DataValidation
--Select Custom from the 'Allow' dropdown and enter the below formula

=COUNTIF($A1:$J1,A1)=1

--From the Error alert tab enter the message you want to be displayed
--Click OK and try.

--
Jacob (MVP - Excel)


"Gotroots" wrote:

Hi,

I need to prevent data from being entered into a cell if there is already
data in any cell left or right of it in the same row.

Thanks
Gotroots