Rob,
I think he want's it to be "greyed out," indicating to the user that it's
not usable under the current conditions. When it's disabled, it turns gray,
and it can't be clicked. Well, it can, but it doesn't do anything - its
checked state doesn't change. Disabling can be done with macro code,
including event code, which gets run automatically when cells are updated,
sheets are changed, or whatever. We'll see what he has to say if he posts
back about his requirements.