Dear all,

o.k., I found the screenupdating function and included it.
Unfortunately this does not the resolve the issue, although it does speed up the macro a little bit.

Furthermore I noticed, that when the macro is running, I cannot UNDO any cell operations any more. This is a great disadvantage towards conditional formatting of course, so I would be very grateful for any constructive ideas...

Thanks to the community!!!

Titus.