Try this ..

Select col B
Click Data Validation
Allow: Custom
Formula: =COUNTIF(B:B,B1)<2
Click OK
--
Max
Singapore
http://savefile.com/projects/236895
xdemechanik
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"Dr Alok Modi MD" wrote:

Hi Sandy
Thanks for replying to me. My problem is different here. See suppose I am
entering various invoice numbers in coumn B. Let us say I have entered the
following 10 invoice numbers :
2342
323
121212
12445
323423
435432
23432
23233
234
2332

No let us say i am about to enter 23432, in (now the cell would be B11),
B11, excel would not tell me that 23432 has been eneterd already. imagine how
this gets complicated if already say 100 enteries have been made. Now when we
enter text instaed of numbers, the moment you repeat text excel enters it
automatically and highlights it. So you know that you have laready entered it.

Can you provide me a similar solution od a solution by which I can get an
error dialogue flash ?

Dr Alok Modi MD