This is what I have coded, I must be missing something.
Private Sub Material_Change()
'If the combo box is cleared, clear the form filter.
If Nz(Me.Combo300.Text) = "" Then
Me.Form.Filter = ""
Me.FilterOn = False
'If a combo box item is seleccted, filter for an exact match.
'Use the ListIndex property to check if the value is an item in the list.
ElseIf Me.Combo300.ListIndex <> -1 Then
Me.Form.Filter = "[Material] = "" &_"
Replace(Me.Combo100.Text, "", """) & ""
Me.FilterOn = True
'If a partial vaslue is typed, filter for a partial material name match.
Else
Me.Form.Filter = "[Material] Like " * " &_ "
Replace(Me.Combo300.Text, "", "") & "*"
Me.FilterOn = True
End If
'Move the cursor to the end of the combo box.
Me.Combo300.SetFocus
Me.Combo300.SelStart = Len(Me.Combo300.Text)
End Sub