The effects of gonadal steroids on the secretion and gene expression of macrophage colony-stimulating factor (M-CSF) and on the secretion of transforming growth factor (TGF)-beta 1 and TGF-beta 2 by human endometrial stromal cells (ESCs) were examined by an in vitro system of ESC differentiation (decidualization). M-CSF production by ESCs was dose-dependently enhanced by the addition of progesterone or testosterone, while estradiol treatment had no effect. TGF-beta 2 secretion by ESCs was inhibited by progesterone, estradiol and testosterone treatment, and on the contrary, slight enhancement by estradiol was observed in TGF-beta 1 secretion. These findings indicate that human ESCs produce cytokines of M-CSF and TGF-beta s, which are important for the growth and differentiation of the peri-implantation embryo as well as local immune cells under direct control of gonadal steroidal actions, and suggest a novel network between endocrine and immune systems in the human endometrium.