Thanks keepITcool. That's very interesting. Unfortunately, I don't think it
is responsible for my problem however. There are only typically about 10
areas involved. I intend to experiment with your suggestion just in case
there is some interaction with the issue you describe and some unknown.

I experimented with not using the Cut method and only hiding/unhiding rows
(i.e. conventional filter/unfilter) and left the Union code the same.
Execution was excellent (< 1 sec) and it did not become progressively slower
with multiple executions. This seems to prove that it is the Cut method that
is the problem. It was also worse when I inserted/deleted cells to move the
contents in an earlier version. As I mentioned, leaving the contents within
the visible range, even if hidden, results in a scrolling problem if there
are enough hidden rows. So this isn't the desired solution.

Best regards,
Greg