In this study we investigated glucose tolerance in relation to autologous bone marrow transplantation (ABMT). In 13 adult patients with acute myeloblastic (AML) or lymphoblastic (ALL) leukaemia in complete remission (CR), intravenous glucose tolerance test (IVGTT) was performed 1 month before and 6 months after ABMT. Patients with AML in CR received, as myeloablative therapy, cyclophosphamide combined with busulphan or total body irradiation (TBI). ALL patients received total body irradiation in combination with vincristine, daunorubicin, Ara-C, cyclophosphamide and prednisone. Before ABMT all patients, in spite of the intensive chemotherapy given for remission induction and consolidation, had a normal glucose tolerance. However, 6 months after the transplantation the k-value (rate of glucose elimination) for this group of patients had decreased (p less than 0.01). The trend towards impaired glucose tolerance was correlated with lower peak insulin values during IVGTT (p less than 0.05). Thus, the myeloablative therapy in connection with ABMT caused an impairment of pancreatic beta-cell function. No patient has hitherto developed clinical diabetes mellitus.