Use conditional formatting with a formula of

=ISNUMBER(MATCH(A1,B:B,0))

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HTH

Bob

"Dan H." wrote in message
...
I have a blank column A and a second column B with different alpha-numeric
17-characters in cells B1 to B50000. These are vehicle VINs.
Now, when I enter a VIN in A1, I would like to find if this VIN is in
column B and, if it is, turn the A1 cell red.
Next, I would enter a new VIN in A2 and again, check to see if it is in
column B and, if so, turn A2 red. I would continue this data entry down in
column A for up to 700-1000 VINs. I'd expect maybe 3-4 matches after
entering
about 1000 VINs in column A.