Phospholipase A2 (PLA2) activity was measured in articular cartilage from normal and osteoarthritic (OA) human femoral heads. Protoglycanase and collagenase activity was determined in the same specimens using radiolabelled human proteoglycan subunit and type II collagen, respectively. Grossly normal and fibrillated OA cartilage samples showed a significant increase in PLA2 activity which was not found in osteophytic cartilage. PLA2 activity was found to be correlated with proteoglycanase but unrelated to collagenase activity. Tiaprofenic acid induced in vitro a concomitant increase in PLA2 and a decrease in proteoglycanase activity. PLA2 which may be activated by cytokines as well as mechanical factors is suggested as a key enzyme in chondrocyte metabolism regulation. Tiaprofenic acid is shown as a potential chondroprotective nonsteroidal anti-inflammatory drug.