In xl2003 and below, you can see 1000 unique values.

Debra Dalgleish has some notes/workarounds:
http://contextures.com/xlautofilter03.html



Ratrace wrote:

I have a very long spreadsheet. I have checked the autofilter dropdown list
and found that not all the items present in the column are listed. I don't
think I have any blank rows. Is there a maximum number of items that will
show up in an autofilter list? If so, is theere a way to change that? If
not, help!

--

Dave Peterson