I've got a form that opens a subform showing related information based on [ClientID]. What I would like to have happen is the subform have a combo box that displays all the values of [CaseID] for matching [ClientID] records. I would then use the combo box to go to the specific [CaseID] record I wanted to view. I've tried using a parameter query as the control source for the combo box, but I can't get the query to automatically accept the [ClientID] value from the original form rather than prompting me for the parameter. Any ideas?

make the parameter like this

=Forms![formname].[ClientID]

Then on the afterupdate of the ClientID field have it run a Requery on the Combo box

Me.[cmbField].Requery