ABSTRACT: The decidua apparently plays a major role in immune tolerance to the semiallogeneic embryo. In the present study we applied the immunohistochemical ABC method to investigate the expression of CD3, TCR α/β and TCR γ/δ molecules on intradecidual T cells with a panel of mAbs. Whereas intradecidual T cells expressed readily detectable amounts of CD3, they lacked immunohistochemically detectable amounts of either α/β or γ/δ TCR heterodimers on their cell surface. Peripheral blood smears of the same patients showed normal expression of α/β and gM/δ TCR on CD3 + T cells. The specific absence of (α/β or γ/δ) TCR molecules on the surface of intradecidual T cells could be one of the decisive factors in tolerance of the maternal immune system towards the fetus.