Set up listbox2 to have a parameterized view for its rowsource (rowsourcetype of alias). Put the view in the DE of the form and mark its NoDataOnLoad property .T..

Now in the Requery of listBox2 put this code;

* Listbox2.Requery()
LOCAL lcParmForView
lcParmForView = Thisform.Listbox1.Value
Requery("TheViewForThisListbox")


Now, whenever the user makes a selection in listbox1 you call the requery for listbox2.