Many thanks to all.

Again, 1,000's of rows.

Need a script to insert a certain number in B if a certain number exists in A

Actually, these are "non-add" part numbers, not really values, but I don't know how else to describe it. [text?]

If A:A=12345, then insert 5678 in B in same row

If A:A=4567, then insert 49509 in B in same row

thanks again!