I don't know how to automatically do it, but you can use conditional
formatting to highlight the ones you need to delete. It might speed things
up a bit until a smarter person tells you how to do it right. :)

1. Highlight Column A
2. Select Format-Conditional Formating
3. Select "Formula Is"
4. Insert
=COUNTIF($B:$B,A1)=0
as your formula
5. Select an obvious formatting like a yellow background color
6. Click Okay
7. Click Okay

All cells that don't have a matching value in column B should now be
highlighted.
Repeat the procedure on column B but use this formula instead
=COUNTIF($A:$A,B1)=0
to highlight extraneous cells in column B.

"doohen" wrote:

I have 2 columns of data. Both should ultimately have identical data,
but both have extranious data I need to separate. These lists will be
300+ long, so by hand is taking forever. Example:
Column A Column B
12345 12344
12346 12345
12347 12346
12348 12347
12349 12349

I need a way to extract the 12344 from column B since it is not in A,
and 12348 from A since it is not in B. They do not have the same number
of entries. Any ideas? Thanks sooooo much in advance!