The effect of various anti-inflammatory drugs on the production of prostaglandins E2 and F2α, 6 keto PGF1α and thromboxane B2 by bovine articular chondrocytes was measured by radioimmunoassay. While indomethacin and meclofenamic acid caused a dose-dependent inhibition of all prostanoids measured, the effects of hydrocortisone and colchicine varied with respect to different prostanoids. Hydrocortisone (10−7M – 10−3M) both in the presence and absence of added arachidonic acid, resulted in an inhibition of prostaglandins E2 and F2, and to a lesser extent, 6 keto PGF1α, but T×B2 production was only slightly inhibited by the drug in the absenced of arachidonic acid and markedly increased in its presence. Colchicine (10−7M – 10−3M) had the opposite effect, causing an inhibition of T×B2 and stimulating PGE2 and 6 keto PGF1α production. These findings suggest that certain anti-inflammatory drugs may, in addition to their action on phospholipase A2 and cyclo-oxygenase, exert potent effects at the level of the different synthetases. In order to see whether these alterations in relative prostanoid levels affected proteoglycan metabolism, the effect of anti-inflammatory drugs on proteoglycan synthesis by cultured chondrocytes was tested using 35SO4 labeling methodology. The results showed that the concentrations tested (10−5M to 10−7M), indomethacin, dexamethasone, hydrocortisone and colchicine inhibited 35SO4 incorporation into newly synthesized proteoglycan molecules both in the presence (10−6M) and absence of exogenous arachidonic acid. In the same concentration range choroquine had no effect.These results do not support the hypothesis of direct prostanoid involvement in the modulation of proteoglycan synthesis in articular cartilage.