During 7 years 81 patients received an allogeneic bone marrow transplant (BMT) for several diseases. The prevention of graft-versus-host disease (GVHD) was undertaken with methotrexate (MTX), MTX plus antilymphocytic gammaglobulin plus prednisone (MTX + ALT + P), and elimination of the T-lymphocytes of the donor's bone marrow with the monoclonal antibody CAMPATH-1. The actuarial survival of the patients who did not develop GVHD was significantly better than that of those who developed grade II-IV GVHD: 56% [95% confidence interval (CI) 39-71%] versus 10% (95% CI 3-25%) (p less than 0.0001). However, actuarial survival was similar in each of the three groups: MTX 35%, MTX + ALT + P 38%, and CAMPATH-1 43%. The incidence of GVH disease, when the sex of the donor and the receptor were different, was significantly higher than in cases where the donor and the receptor had the same sex: 45% (95% CI 31-58%) vs 15% (95% CI 8-28%) (p less than 0.005). By contrast, significant differences were not found between the three groups in the incidence of GVHD: MTX 36%, MTX + ALT + P 34%, and CAMPATH-1 20%. In patients with leukemia, a higher number of relapses occurred in the MTX group, because a higher number of patients in second or third complete remission (CR) or with active disease underwent transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)