Using in vitro methods, we have determined the effects of four NSAIDs on the biosynthesis and turnover of proteoglycans in articular cartilage explants. Over the concentration ranges examined (5 X 10(-7) to 10(-5) mol/L for tiaprofenic acid, naproxen and indomethacin; 5 X 10(-5) to 10(-3) mol/L for aspirin), all the drugs examined, except tiaprofenic acid, reduced the rate of proteoglycan synthesis compared with control tissue. All of the compounds examined reduced the turnover rate of newly synthesised proteoglycans. The products of turnover of explants treated with the various NSAIDs did not appear to be significantly different from those produced by control tissue, as assessed by gel chromatography and electrophoresis. There were some indications, however, of quantitative differences in distribution on both these analytical systems. These results indicate that with the exception of tiaprofenic acid all the NSAIDs examined produced a general reduction in chondrocyte metabolic activity. Thus it seems unlikely that tiaprofenic acid would have a direct detrimental effect on articular cartilage during long term administration.