Finding repeated data in adjacent cells

Hi,

This is probably a very simple question, but I am fairly new to Excel and have not been able to solve it.

I'd like Excel to find repeated data in adjacent cells (to see if we have accidently re-used an account number).

Anyone know how this is done?

Thanks in advance-

Say that the values you want to check for duplicates in is in Column A. In column B have this formula =IF(COUNTIF($A$1:$A$1000,A1)>1,"DUPLICATE","")

Is there an easy way to have the word DUPLICATE kicked out in Column B only where a duplicate is found in Column A? Right now it seems like the formula tells me a duplicate exists in column A, but I am hoping to be able to find the duplicates automatically.

Thanks again for your help-

Now I got it - the function has to be in each cell in column B. Thanks for the help Kraljb. Saved a lot of time...