Excel Help please - comparing columns

I'd use 2 lookups to idenitfy where the same code exists in the other column and vice versa, then filter on nonblanks to highlight the ones where there are duplicates

HTH

I might use conditional formatting. Activate the first cell in Column B, go to formatting, conditional formatting, then set a formula to say something like =countif(A:A,B1)=0 (I don't have excel on this pc so I can't remember whether that's rigthti. Then set the conditonal format to highlight the cell if that formula is true.

Not sure if that makes sense.

Thanks both, I've done it the conditional formatting way and it seems to have worked - couldn't get my head round the lookup function in this case.