We evaluate the chondrotoxic effects of some nonsteroidal antiinflammatory drugs (NSAIDs) on articular cartilage in an experimental model of osteoarthritis (OA). Each of 30 Sprague-Dawley rats weighing 0.250 kg and 12 weeks old received weekly injections of sodium iodoacetate (1 mg/0.1 mi NaCl) in the right knees for 8 weeks to induce an experimental model of OA. The left knees served as controls. Four groups were formed of ten rats each. The control group received no medicine. In the other three groups, tiaprofenic acid, diclofenac, and indomethacin were given orally for 12 weeks. At the end of the 20th week, the complete groups were sacrificed and histologic evaluation performed. In the right: knees of the control group, specific morphologic changes for OA were observed. Of the three NSAIDs tested, indomethacin was found to have deleterious effects on articular cartilage of both left and right knees. Diclofenac caused a statistically significant increase in the severity of most of the osteoarthritic parameters that were examined in the right knees, whereas tiaprofenic acid was observed to have some beneficial influences on the articular cartilage of right knees, Both diclofenac and tiaprofenic acid displayed the same deleterious effects on articular cartilage of left knees. We conclude that, in the prescription of NSAIDs for OA, it would be appropriate to choose a drug with a protective effect on chondrocytes and articular cartilage.