Dear Hilary, thank you very much for your reply.
Yes, it's a Sharepoint list form (customized with InfoPath). I know how to filter dropdown menu choices based on antoher list, but I think you are saying a different thing here.
I can create a different display form for my list, but how can I execute the query when I click on the title of one item? Would you kindly give me some instrucions on how to do that?
Thanks a lot.