Flurbiprofen, a nonsteroidal anti-inflammatory drug (NSAID), reduces bone resorption in periodontal disease. This therapeutic effect has been attributed to inhibition of prostaglandin synthesis. In view of the importance of carbonic anhydrase (CA) in bone resorption, we examined the CA-inhibitory properties of flurbiprofen using bovine and human CA II and compared them with those of acetazolamide and two other NSAIDs, ibuprofen and indomethacin. Flurbiprofen inhibited both human and bovine erythrocyte CA II but to a much lesser degree than acetazolamide. Ibuprofen and indomethacin were much less active in inhibiting CA II than flurbiprofen.