Two nonsteroidal antiinflammatory drugs (NSAID: acetylsalicylic acid, ASA, and tiaprofenic acid, TA) were tested on differentiated human chondrocytes cultivated in clusters. DNA synthesis was depressed by ASA at therapeutic concentrations. The amount of proteoglycans in culture medium was decreased by ASA, whereas type II collagen was not modified. By contrast, TA did not affect chondroformative processes in chondrocytes. Both NSAID were potent inhibitors of prostaglandin E2 (PGE2) synthesis, TA being more efficient than ASA. From these experiments, we conclude that TA and ASA inhibit PGE2 synthesis; TA did not depress chondroformative variables in human cartilage in vitro, while ASA induced a decrease of DNA and proteoglycan syntheses.