Steve-
I think you need to refresh the control after you change the controlSource.
Also, I've got to ask: why are you changing the case in LostFocus when your Format is/should be handling that for you?

>I have several editboxes on assorted pageframes on a form. Some of the UPPER (change text to all caps within the editboxes) commands work and some don't.
>
>Here is one editbox example:
>
>In the LostFocus Event of the editbox I have -
>REPLACE mytable.myfield WITH UPPER(mytable.myfield)
>
>For properties I have -
>ControlSource = mytable.myfield
>Format = !K
>Read Only = .T.
>Enabled = .T.