The effect of B protaglandins (PG) on growth and sulfate incorportation by monolayer and spinner-cultured rabbit articular chondrocytes has been measured. PGA1, PGB1, PGE1 and PGE2 reduced synthesis of sulfated glycosaminoglycans (GAG) but the PGF series did not. PGA1 was the most potent, being effective at a concentration of 2.5 microng/ml [6.8 micronM] while the others required 25 microng/ml. These compounds had no effect on degradation of GAG. All 8 PGs augmented growth slightly but significantly at 2.5 microng/ml. At the higher concentration, PGA1 was highly cytotoxic, and PGB1 as well as PGE2 reduced cell growth. The cytotoxicity of PGA1 was also observed in two additional types of cultured connective tissue cells, but the inhibition of sulfated-GAG synthesis by PGA1 and PGB1 was confined to the chondrocytes. The response of cultured chondrocytes to exogenous PGs, albeit at apparently unphysiologically high concentrations, together with other evidence, suggests that these compounds may conceivably play a direct role in cartilage metabolism in vivo.