Supernatants from the P388D1 macrophage cell line as well as human interleukin-1 (IL-1) stimulated primary rabbit articular chondrocytes to produce collagen- (C-ase) and proteoglycan- (PG-ase) degrading proteases. The P388D1 derived factor had a molecular weight of 16,000-20,000 and a pI of 4.5-5.0. Both protease activities were metal dependent and inhibited by EDTA, phenanthroline, and alpha 2-macroglobulin but not by PMSF, TLCK, pepstatin, or alpha 1-antitrypsin. Size exclusion chromatography indicated the molecular weights for latent PG-ase and C-ase were 44,000-56,000 and 34,000-44,000, respectively. Chemical synthesis efforts produced two classes of C-ase inhibitors--thiols and hydroxamic acids. The former had IC50 values of 10(-5)-10(-6) M while the latter approached 10(-7) M.