Incubation of human chondrocytes with interleukin-1 beta, tumour necrosis factor or endotoxin induced the expression of NO synthase. The synthesis of NO induced by IL-1 beta was concentration- and time- dependent, occurred after a lag period of approximately 6h and was inhibited by NG-monomethyl-L-arginine, cycloheximide, dexamethasone and hydrocortisone, but not by indomethacin. The activity of NO synthase from activated chondrocytes was not affected by EGTA or by the calmodulin inhibitor W-13. Northern blot analysis, with a rabbit chondrocyte inos probe, showed a 4.4kb positively hybridising band from activated human chondrocytes. Thus, human articular chondrocytes express an inducible NO synthase from the same family as the rabbit chondrocyte and rodent macrophage enzymes. This family appears to vary in terms of in vitro Ca(2+)-dependence and sensitivity to glucocorticoids.