I've not actually tried removing a 'border' from a JComboBox, but I've
noted that the edge of JButton's in Metal can be removed by using
setBorder(null) .  I assume you are trying to create a combo box without
any actual box defining its area?  If the combo box component doesn't
use a Border to draw its edges (like JButtons clearly do) then you'll
have to resort to subclassing JComboBox or creating your own PLaF for
that specific component type.

-FISH-   ><