Find duplicates across columns in Excel

=ISNUMBER(MATCH(A1,B$1:B$20,FALSE))

will return TRUE if the name in A1 is in the range B1:B20. Enter it in say C1 and copy down as far as necessary. If you AutoFilter the data for column C = TRUE you will see which rows to delete.

src: http://www.mrexcel.com/forum/excel-questions/55208-identify-duplicates-between-2-columns.html