Hi Mike,

If I understand correctly, you'd like the cell choices in your matrix to be
1,2,3,4, or blank.  When you create your validation list, I think all you
need to do is ensure that the "Ignore blank" check box is checked on (your
validation list would just be the usual "1,2,3,4").  If you truly want to
change one of the current numerical entries in your matrix to a blank, just
place focus on the cell and hit your delete key (since the validation will
permit blanks).  The other possible way to do this would be to set a
validation list of "0,1,2,3,4" and then open the Tools|Options dialogue box,
select the "View" tab, and then uncheck "Zero values".  In this case, if you
choose a zero value from the validation list in any cells in the matrix, it
will actually display as blank.  The only caveat with this approach is that
it will affect the entire worksheet in which your validation matrix is
located (so, if you want to see potential zero values outside of your matrix,
this wouldn't be the way to go).  Hope this helps.

Paul