To determine the influence of advanced age on long-term survival after allogeneic bone marrow transplantation (BMT), the probability of survival and the frequency of transplantation-associated complications were analysed retrospectively in 20 patients with acute leukaemia (AL) or chronic myeloid leukaemia (CML), who were 40-49 years of age (median 44.5 years) at the time of transplant. The results of this patient group were compared to those of 32 patients aged 30-39 years (median 33.5 years) with AL or CML, who also underwent BMT during the same period of time. The overall actuarial survival of the two age groups was comparable with 44% and 41% at 5.9 and 5.6 years, respectively. Patients with standard risk criteria (i.e. HLA-genotypically identical sibling donor, 1st chronic phase of CML or 1st remission of AL) showed a higher probability of survival in both groups (62% at 5.9 years in older patients and 59% at 5.5 years in younger patients, respectively). In contrast, actuarial survival in patients who underwent BMT at an advanced stage of their disease or with marrow from a partially HLA-compatible donor was significantly inferior (P = 0.04). The cumulative incidence of acute and chronic graft-versus-host disease was low in older patients (27%), who received marrow from an HLA-identical sibling donor. The most frequent cause of death was interstitial pneumonia, occurring in seven of the older patients (35%) and in seven of the younger patients (22%). This difference, however, was not statistically significant. Our results indicate that allogenic marrow transplantation in the fifth decade of life might be associated with a tolerable risk of transplantation-related complications. This treatment modality may therefore be regarded as first-line therapy for patients in 1st remission of AL or first chronic phase of CML, who show a normal performance status. The same applies to older patients in advanced stages of disease, since the results are comparable to those achieved in the younger patient group.