A simple way to do this is to make the tabular form a subform then on the
mainform, use the combo box as the LinkMasterField and use the related field
in the LinkChildField of the subform. This way Access will always filter
the subform for you based on the selected value in the combo.
Otherwise, you would need to use the AfterUpdate event to either set and
apply a filter to the form or modify the form's Recordsource query to use
the combo's value in the Where Criteria.
For example, if your combo was used to filter a ...