You can try the countif function as follows:

In file 1 add a formula in a blank column to be =countif($A$1:$A
$100,a1)

Modify the range to be what ever you need

Any value returned by countif 1 is a duplicate.

On Nov 11, 7:09 pm, JCM wrote:
I have two files with about 10,000 rows. Each one has a column that has
duplicates in each column so conditional formating does not help me find a
duplicate between the files. I would like to add a column where I can
indicate which values are duplicates between the two files. Access will not
work because there is no common link. I would like to have a value which
indicates which rows are duplicates so I can sort them and get them to the
top of the file.