>I have this form with a cbo. This cbo is allowed to remain empty. If the user moves forward without modifying then alls well.
>
>Now supposing the user makes a selection and then he doesn't want it, how can he undo his selection. This cbo is connected to a lookup master database, as soon as the selection is made the FK in this table is updated with the PK from the lookup master.
>
>Except reverting changes is there any solution. Please advise.

How does the user "signal" he does not want the selection? Maybe you could trap the {ESC} key having been pressed, in the valid or lostfocus of the cbo. Then empty out the FK, and the cbo (visually).