Twenty patients aged 27-47 years (median, 35 years) with hematological malignancies, treated with T cell-depleted bone marrow transplantation received in a pilot study five donations of 15 Gy irradiated donor buffy coat cells at days +1, +3, +5, +7, +14 in order to prevent rejection and leukemic relapse. Patients were conditioned with etoposide, cyclophosphamide and 12 Gy fractionated total body irradiation and given cyclosporine postgrafting. Donor bone marrow was T cell-depleted (median 3% remaining T cells) by counterflow elutriation. All patients engrafted. Fourteen (70%) are alive. Two are living with relapse, 12 (60%) are alive and well without any signs of disease, 2-27 months (median, 9 months) post-transplant. Three patients died of interstitial pneumonitis and/or graft-versus-host-disease; three died of relapse. This pilot study supports previous animal data. Repeated infusions of 15 Gy irradiated donor buffy coat are feasible and do not appear to increase transplant related mortality. Whether this approach ultimately will reduce the rate of rejection and relapse following T cell depletion needs to be confirmed in a larger, prospective study.