Human endometrium expresses TGF-beta and TGF-beta receptors where they regulate several endometrial biological activities implicated in embryo implantation, irregular bleeding, endometriosis, and cancer. In the present study, we determined the expression of Smads, intracellular signals that mediate TGF-beta receptors signals from the cell surface to the nucleus, in the endometrium as well as isolated endometrial epithelial (EEC) and stromal (ESC) cells. We also determined whether TGF-beta regulates the expression Smads and activates Smad3 in these cells and endometrial surface epithelial cell line (HES). Using semiquantitative RT-PCR, Western blot analysis, and immunohistochemistry, we found that endometrium, EEC, ESC, and HES express Smad3, -4, and -7 mRNA and protein and contain phosphorylated Smad3 (pSmad3). Smads and pSmad3 were localized in the epithelial and stromal cells with cytoplasmic/nuclear localization. TGF-beta in a dose- and time-dependent manner increased the expression of Smads mRNA and protein, the rate of pSmad3 activation, and Smad3 translocation into the nucleus in ESC and HES. The effect of TGF-beta on pSmad3 induction was, in part, abrogated by the pretreatment of HES and ESC with TGF-beta type II receptor antisense oligonucleotides. We conclude that human endometrium expresses the necessary components of Smad signaling pathway, whose expression and induction in endometrial epithelial and stromal cells are regulated by TGF-beta.