I think it's pointing me in the right direction. It doesn't do what I want - display the listbox part of the combobox - but it misbehaves on my system in a different way from my code. The listbox (when first shown) appears only where it is longer than the mainwindow. After that, it's fine. This leads me to the conclusion that JComboBox is using a geometry manager that doesn't like the things I am doing. I've tried a few things that haven't worked, but I'm going down this route first. I'll try to see what's happening in the source. However, I looked at the node zentara pointed me at and didn't really understand the issues, so I may be biting off more than I can chew. But I have at least got something I can try, so thank you both for that. I'll report back if I get anywhere.

Regards,

John Davies