I don't use macros... ever.
BTW, "NC ref #" is an extreamly poor field name. It has spaces in the name and a special character (which happens to be a date delimiter).
Better would be "NC_RefID_PK" for the primary key and "NC_RefID_FK" for the foreign key field.
In VBA, it would be something like this:
Code:
Private Sub btnOpenSubForm_Click()
DoCmd.OpenForm "MySubForm", , , "[NC_RefID_FK] = " & Me.NC_RefID_PK
End Sub
Change "MySubForm" to the name of your sub form.
"btnOpenSubForm" is what I named the button.
The macro *might* be like this (again, I never use macros, so this couold be way off):