In a retrospective analysis of T cell depleted bone marrow transplantation, we have looked at different parameters in order to determine risk-factors of graft-failure after allogeneic bone marrow transplantation for leukemia. Fifty-one patients with acute leukemia or chronic myeloid leukemia have been analysed. For 33 of them, the pretransplant conditioning regimen consisted of fractionated total body irradiation (TBI) at 12 Gy prior to cyclophosphamide (120 mg/kg). The other patients received various reinforced preparative regimens. T-cell depletion consisted of treating marrow cells with pan-T monoclonal antibodies (CD2+CD3 or CD2-CD5-CD7) followed by complement mediated cytolysis. No post-transplant immunosuppressive prophylaxis was administered except for the first nine patients who received Methotrexate alone. In this group of 51 patients, 12 died within 3 months from graft-related complications and 10 developed graft failure (no engraftment or rejection). Among the possible risk factors associated with this failure, two graft-related parameters appeared significant: the number of CFU-GM progenitors and the number of viable T cells injected with the marrow inoculum. No correlation with graft failure was found with other parameters including diagnosis, disease status at transplant, conditioning regimen, age, sex, and CMV status of donor/host pairs. However, the interpretation must remain cautious because of the relatively small samples in each group.