RE: Combobox choices depends on another combobox (cascading dropdown) Carl Tyler 12.Oct.17 10:12 AM Lotus Notes Domino Designer All ReleasesWindows XP
Jheng's answer whilst correct is not really complete.
You can use a formula, the key thing you need to do however is mark the refresh fields on keyword change. You can find more help on that setting in the Domino Designer Help, or using google. Without that field option , the combobox choices won't change until you save and reopen the document.