It is known that in the course of osteoarthritis (OA), articular cartilage develops biochemical and structural changes. In the last years, serum and urinary markers of both the synthesis and destruction of cartilage have been dosed, above all in order to carry out an early diagnosis of OA. Among them, the urinary excretion of pyridinoline seems to correlate with the entity of the degradation of cartilage. The aim of the present study is to evaluate the above mentioned markers in OA patients compared to control subjects. Moreover, the possible influence on cartilage of two different non steroidal antiinflammatory drugs (NSAIDs), in particular Nabumetone and Piroxicam, has been verified. The study shows that the urinary excretion of pyridinoline is able to express the severity of OA. At last, the study shows that the tested drugs do not interfere with the metabolism of cartilage.