We have previously demonstrated that hGH stimulates DNA synthesis in cultured chondrocytes in the absence of serum. The present study is concerned with the effects of hGH on proteoglycan synthesis by cultured chondrocytes. Chondrocytes were isolated from rat rib growth cartilage by collagenase digestion, plated in plastic dishes, transferred to serum-free MCDB 104 medium, and incubated for 24 h to establish growth arrest. The cultures were then preincubated for 0-24 h with various concentrations of hGH and ovine prolactin (oPrl) and finally pulse-labelled for 30 min with radioactive sulphate in the presence of hormone. hGH, but not oPrl, stimulated sulphate incorporation with an apparent maximum at 50 ng/ml (approximately 170%). The stimulatory effect was apparent after 2 h and maximal after 3h preincubation. After 12 h the stimulatory effect had decreased to insignificant levels. Qualitative analysis of isolated proteoglycans indicated that the stimulation of sulphate incorporation by hGH is exerted at the level of protein synthesis with little effect on glycosylation and sulphation. Further experiments are required to demonstrate whether the stimulatory effect on proteoglycan synthesis is a specific phenomenon or represents one aspect of a general stimulation on cell metabolism in preparation for DNA synthesis.