At Huddinge Hospital 275 patients underwent allogeneic bone marrow transplantation. Among children in first remission of acute leukemia or chronic phase CML (early leukemia), with HLA-identical marrow the 8-year leukemia-free survival was 77%. This was better than 38% in children undergoing transplantation in second to fourth remission (p less than 0.0009). In adults with early leukemia, the 8-year leukemia-free survival was 47% compared to 21% for intermediate-risk adults (p = 0.007). Among 25 patients with severe aplastic anemia receiving marrow from HLA-identical siblings, the actuarial 10-year survival was 78%. In 14 patients with various metabolic disorders, of whom half received marrow from HLA-mismatched donors, the actuarial 7-year survival was 71%. Forty-three patients were given marrow from HLA-mismatched donors and had an increased incidence of acute graft-versus-host disease (GvHD) and death due to GvHD compared to recipients of HLA-identical bone marrow. The major causes of death among our patients were relapse of leukemia, death due to GvHD, cytomegalovirus (CMV) pneumonitis, bacterial infection and invasive fungal infections. By preventing GvHD with T-cell depletion or methotrexate (MTX) combined with cyclosporine (CsA) acute GvHD decreased, but the incidence of relapse increased compared to patients treated with MTX or CsA alone. This resulted in improved survival in patients older than 30 years, but a nonsignificant decrease in leukemia-free survival in younger patients. There was an association between herpes virus immunity in the recipient and GvHD. CMV pneumonitis increased following GvHD and decreased in patients treated with MTX combined with CsA. Invasive fungal infections may be treated or prevented using amphotericin B encapsulated in liposomes with few side effects.