The well known nonsteroidal antiinflammatory drugs (NSAID) diclofenac, piroxicam and tiaprofenic acid as well as the corticosteroid prednisolone, were examined for their effect on injury to knee joint structures evoked by a developing murine antigen induced arthritis. To ensure the human therapeutic dose, each drug was given twice a day per os in 3 different dosage regimes. The severity of arthritis was monitored with 99mTc-uptake measurements. After 3 weeks, mice were sacrificed and knee joints were examined histologically. All drugs exhibited, in comparable extent, antiinflammatory effects in terms of swelling. Grading of joint damage was focused on cartilage harm and chondrocyte activity. Only prednisolone provided sufficient protection and seemed to stimulate repair activity. The NSAID had no clear beneficial or adverse influences on affected cartilage. Apparently, under these experimental circumstances, only prednisolone functions chondroprotectively.