Twenty-five patients with hematologic malignancies were treated with busulfan (16 mg/kg) and cyclophosphamide (50 mg/kg x 3 days) as conditioning for bone marrow transplantation using marrow from serologically matched, DR locus genotypically identical unrelated donors. Previous studies of BuCy2 as conditioning for UD-BMT have reported a graft failure rate of up to 21% suggesting it may be insufficiently immunosuppressive in this setting. We elected not to use BuCy4 as it may have a higher incidence of extramedullary toxicity. In addition the patients received GM-CSF (500 mg/m2) from day 0, cyclosporine and short-course methotrexate (15 mg/m2 x 1, then 10 mg/m2 x 3) as GVHD prophylaxis and prophylactic ganciclovir at engraftment if either they or their donor were CMV antibody positive. The median age of the 25 patients was 41 years and the most common diagnosis was CML (76%). Seven patients were considered poor risk and eight males were recipients of marrow from female donors. Sixteen patients survive at a median of 435 days from transplant. The actuarial overall and disease-free survivals at 1 year in this group of older patients were 62 +/- 20% and 57 +/- 20% and 100-day survival was 70%. The engraftment rate was 100%; there have been no instances of secondary graft failure. Fifteen patients (60%) developed grade II-IV GVHD and 12 of 16 (75%) developed some chronic GVHD but only half of these were extensive. The performance status of survivors is good (median of 90); seven of 12 eligible patients are back at work. This study demonstrates that UD-BMT can be successfully performed in very closely HLA-matched older patients using a chemotherapy-only protocol and that low rates of severe acute GVHD can be achieved without T cell depletion.