In C2 place the formula
=IF(ISNA(VLOOKUP(B2,$D$2:$D$100,1,0)),"","X")
and copy down.

Hope this helps
Rowan

"Jane" wrote:

here is my data:
col A col B col C col D
store# row sampling #
3 1 210
5 2 5
7 3 11
10 4 510
12 5 X 42

I want to be able to make an "X" in column C if the row # in column B is
also located in column D in the case of store # 12 above, otherwise have the
cell in C remain blank.

thank you in advance! jane