In order to assess the immune mechanisms triggered by an immunosuppressive regimen consisting of prophylactic antilymphocyte globulin plus low-dose cyclosporine A and steroids, we studied the short-term evolution of both, anti donor in vitro alloresponse and peripheral blood T cell subsets in 21 recipients of a cadaveric kidney allograft. Spleen cells from cadaveric donors and peripheral blood lymphocytes from the respective recipients pretransplant (pre-Tx), at three and six months posttransplant (post-Tx) were obtained to perform one-way mixed lymphocyte cultures and flow cytometry analysis of lymphocyte subsets. The results indicated the development of donor-specific mixed lymphocyte culture (MLC) hyporesponsiveness as early as three months post-Tx, paralleled by a decrease in CD4+ CD29+ helper-inducer cells and by an increase in CD8+ CD45RA+ suppressor lymphocytes in peripheral blood. These changes were reflected in a very good clinical outcome of the patients. The present results further suggest that suppression of the immune system just before transplantation is a suitable method to induce early specific hyporesponsiveness to the allograft.