Amy
I may be reading too much into your description, but it sounds like you are
trying to do this in a table. If so, DON'T! Don't use the "lookup" data
type in your tables (see the tablesdbdesign newsgroup for examples of why
not... and check the mvps.org/access web site for more reasons not to).
Access tables store data, Access forms display it. Use "cascading combo
boxes" (see the mvps.org/access web site for more) in a form.
And for the record, I don't believe it is possible to do that (base one
combo box on another in a table).
Regards
Jeff Boyce
Microsoft Office/Access MVP