I think Peco knows more about this than I do, but for what it's worth when I specify just the columns, not the rows, I've never noticed my VLOOKUPs slowing down. I've noticed it when I'm doing a lot of VLOOKUPs, of course, thousands instead of dozens. My guess would be that Excel knows the last used row for each worksheet, and never bothers to look below it.

But then, as I said, if Pecoflyer says it'll slow it down I'm not inclined to scoff. Why do you say so, Peco? I've never done benchmarks, only watched for it. (And come to think of it, I always use whole columns; maybe the reason I never notice Excel slowing down is that I have nothing to compare it to.)