Bone marrow transplantation (BMT) has had an increasing role in the treatment of acute nonlymphoblastic leukaemia (ANLL). A review of patients transplanted between May 1975 and August 1991 was undertaken in order to evaluate problems and outcome, and examine the role of both autologous and allogeneic BMT at various stages in the treatment of ANLL. Forty-seven patients received either an allogeneic (n = 24) if a suitable donor was identified or autologous (n = 23) BMT if there was no allogeneic donor. Conditioning therapy consisted of total body irradiation (TBI) and cyclophosphamide (n = 14) or busulfan and cyclophosphamide (n = 33) with or without melphalan. Graft-versus-host disease prevention was with methotrexate (n = 9), methotrexate and cyclosporin (n = 10) or T cell depletion (n = 5). Minimum follow-up for surviving patients was 24 months (median 65 months). For patients transplanted in first remission there was a 0% and 9 +/- 6% transplant-related mortality, a 37 +/- 11% and 33 +/- 12% relapse risk and a 63 +/- 11% and 63 +/- 12% event-free survival for autologous and allogeneic BMT, respectively. In second remission, there was a 14% mortality, 50 +/- 20% relapse risk and 43 +/- 19% event-free survival for allogeneic BMT. No patient transplanted in relapse survived. In patients who survived greater than 24 months, late side effects were noted in all 8 (100%) patients given TBI and in 2 of 19 (10.5%) given busulfan.(ABSTRACT TRUNCATED AT 250 WORDS)