Explants of immature bovine articular cartilage were exposed to nalidixic acid, pipemidic acid and cinoxacin at one and ten times the human therapeutic plasma level for 7 days. Only nalidixic acid had significant effects on the chondrocyte metabolism. 20 micrograms/ml nalidixic acid caused an increase of 35S-sulfate incorporation into glycosaminoglycans at day 7. Two hundred micrograms/ml nalidixic acid inhibited the incorporation of 3H-thymidine into DNA. The incorporation of 35S-sulfate into glycosaminoglycans was decreased at day 0, while at day 7 the incorporation had returned to the control value. Pipemidic acid and cinoxacin had no significant effects on either the 3H-thymidine or the 35S-sulfate incorporation.