To examine the possibility that cytokines produced in inflamed joint tissues may contribute to the loss of articular cartilage by causing inhibition of synthesis of cartilage-specific matrix macromolecules, we studied the effects of interferon gamma (IFN gamma) and tumour necrosis factor alpha (TNF alpha), alone and in combination, on the expression of the genes for types-II, -IX and -XI collagens in cultured human chondrocytes. Chondrocytes isolated from human fetal epiphyseal cartilage by sequential enzymic digestions were cultured in the presence of IFN gamma (30 pM), TNF alpha (15 pM) or a combination of suboptimal concentrations of both cytokines (1.5 pM IFN gamma plus 0.3 pM TNF alpha). IFN gamma caused a maximal decrease of 23.3-32.6% in the biosynthesis of collagen by chondrocytes. TNF alpha was a more potent inhibitor causing a 42.8-45.3% decrease at one-half the concentration of IFN gamma. A synergistic inhibitory effect of 58.2% was observed with the combination of 1.5 pM IFN gamma plus 0.3 pM TNF alpha. Electrophoretic analysis of the biosynthesized proteins showed a co-ordinate decrease in the production of the three cartilage-specific collagen types II, IX and XI. These effects were accompanied by parallel changes in the steady-state levels of their corresponding mRNAs. In vitro transcription assays showed that the collagen inhibitory effects of the cytokines occurred largely at the transcriptional level. Similar effects of the cytokines were observed on biosynthesis of types-II, -IX and -XI collagens and steady-state mRNA levels for type-II collagen by chondrocytes obtained from adult articular cartilage. These observations indicate that IFN gamma and TNF alpha can induce a synergistic inhibition of the synthesis of cartilage-specific collagens by fetal and adult human chondrocytes and suggest that these effects may contribute to the articular cartilage loss that occurs in inflammatory joint diseases.