Although human endometrial adenocarcinoma tissues express high levels of activin A, the pathophysiological functions of endometrial activin A remain unclear. Human endometrial cancer cells express both activin receptor and TGF-beta receptor, and TGF-beta1 utilizes the same intracellular signaling molecules as activin A. Using three differentiated human endometrial adenocarcinoma cell lines, we investigated whether there are interactions between TGF-beta1- and activin A-mediated signaling. Flow cytometric analysis revealed cell surface expression of two types of TGF-beta receptor subunits and four types of activin receptor subunits. TGF-beta1 inhibited cell proliferation in three endometrial adenocarcinoma cell lines. Activin A did not affect the growth of the three endometrial cell lines, and pre-incubation with activin A dose-dependently reduced TGF-beta1-mediated inhibition of cell growth. These results suggest that in endometrial adenocarcinoma cells, the intracellular signals underlying TGF-beta1-mediated inhibition of growth can themselves be inhibited by activin A. Therefore, the increased expression of activin A may be involved in carcinogenesis by reducing TGF-beta-mediated signals inhibiting cell growth in human endometrial adenocarcinoma tissues.