We have examined the mitogenic potential of platelet-derived growth factor (PDGF) on AIDS (acquired immune deficiency syndrome)-related and sporadic Kaposi's sarcoma cells in comparison to fibroblasts at physiological and subphysiological calcium concentrations of the culture medium. At low calcium concentrations in the presence of 3% human serum the growth rate of fibroblasts and Kaposi's sarcoma (KS) cells is similarly reduced to less than half of the growth rate at physiological Ca2+ concentrations. In the presence of 3% PDGF depleted, platelet poor plasma-derived serum (PPPS) growth of KS cells ceased completely, whereas fibroblasts made 1-2 cell divisions within 15 days. At physiological Ca2+ concentrations, the reduced PDGF content in 3% PPPS had no effect on human embryonal fibroblasts and little effect on adult skin fibroblasts. In contrast, KS cells became growth-arrested after one to two doublings. This is consistent with the observation that PDGF B-chain mRNA could not be detected in our KS cells whereas PDGF receptor mRNA was expressed.