Two cell culture systems composed of rat peritoneal macrophages and 2BS fibroblasts were used to study the inhibitory action of tetrandrine on collagen and glycosaminoglycan synthesis. The activation of silica-treated macrophage supernatants stimulated collagen synthesis by 2BS fibroblast cells. Tetrandrine had an inhibitory effect on the biosynthesis of collagen and glycosaminoglycans. The increase in the content of hydroxyproline, representing collagen, was verified by comparing it with that of DNA.