The effects of androgen and glucocorticoid on the proliferation of SC-3 mouse breast carcinoma cells and their mechanisms were investigated in a serum-free culture. Both physiological concentrations of testosterone ( T) and pharmacological concentrations of dexamethasone ( Dex) significantly increased the cell proliferation. The growth-stimulatory effects of two hormones were mediated through their own receptors.SC-3 cells stimulated by T and Dex were also found to secrete fibroblast growth factor (FGF) like factor into conditioned medium (CM) . The addition of anti-FGF antibody in the medium inhibited T, Dex and bFGF-induced proliferation of SC-3 cells. Furthermore, the presence of FGF receptors in SC-3 cells were demonstrated. These results indicated that androgen and glucocorticoid-in-duced enhancement of SC-3 cell growth is mediated through an induction of FGF-like growth factor which acts on SC-3 cells as an autocrine growth factor.