The present study was designed to investigate the potential role of heme as a direct inhibitor of cartilage metabolism and growth. We used the embryonic chick pelvic rudiment bioassays and the hypophysectomized rat cartilage sulfation bioassay, both sensitive to growth factors and growth inhibitors. In the chick bioassay pelvic rudiment growth was inhibited when heme was added to the culture medium at 0.1 mmol/L (after five days in culture, cartilage weight 224% +/- 11% of initial with normal serum, but 141% +/- 3% of initial with serum plus heme 0.25 mmol/L); the heme-induced growth inhibition was promptly reversible when cartilages were placed in heme-free medium. This was due, at least in part, to heme-induced inhibition of (1) [35S] sulfate incorporation into proteoglycans by as little as 0.05 mmol/L heme (66% +/- 5% of assay buffer); (2) [14C] leucine incorporation into proteins by greater than or equal to 0.05 mmol/L heme (85% +/- 6% of assay buffer); and (3) [3H] uridine incorporation by greater than or equal to 0.10 mmol/L heme (50% +/- 4% of assay buffer). In the rat cartilage sulfation bioassay (the literature "standard" bioassay for skeletal growth studies) a dose-dependent inhibition of [35S] sulfate incorporation occurred with greater than or equal to 0.01 mmol/L added heme (82% +/- 3% of assay buffer). Heme caused a dose-dependent and reversible inhibition of cartilage metabolism and growth, and it may have a novel role in the pathophysiology of growth retardation associated with some chronic disease.