During the years 1981-90 inclusive 227 patients with haematological malignancy received an HLA-identical sibling first transplant at St Vincent's Hospital, Sydney. Recipients with acute leukaemia in first remission or chronic myeloid leukaemia in first chronic phase were analysed as good risk, and those beyond these stages, as poor risk patients. Good risk patients transplanted in the years 1986-90 (n = 52) showed improved actuarial survival (74%) compared to those (n = 58) transplanted during 1981-85 (37%, p = 0.01). There was a suggestion that leukaemia-free survival was also improved in those transplanted during the later time period (62% versus 36%, p = 0.07). In contrast, poor risk patients transplanted during 1986-90 (n = 55) appeared to have worse leukaemia-free survival (15%) compared to those transplanted during 1981-85 (n = 62) (22%, p = 0.09). The incidence of acute graft-versus-host disease (GVHD) grades I-IV in all patients was 94% in those transplanted during 1981-85 (n = 120) and 86% in those transplanted during 1986-90 (n = 107) (p = 0.002). The incidence of acute GVHD grades II-IV was 37% during 1981-83, 20% during 1984-86, and 28% during 1987-90 (p = 0.1). The decrease in incidence and severity of acute GVHD correlated with the introduction of the cyclosporin/short methotrexate regimen in our practice. The incidence of cytomegalovirus (CMV) pneumonitis was 18% in 1981-85, and 11% in 1986-90 (p = 0.09). In 1989 and 1990 no cases of CMV pneumonitis occurred.(ABSTRACT TRUNCATED AT 250 WORDS)