Thirty-eight patients (⩾ 18 years) receiving marrow transplants from HLA-identical or one antigen-mismatched related donors were randomized to intraosseous (io)+ intravenous (iv)(n= 10), io (n= 8) or iv (n= 20) infusions of bone marrow. There were no significant differences in patient characteristics. PMN/l more than 0.5× 10 9 occurred on days 19 (median), 20 and 18.5 in the io+ iv, io and iv groups, respectively. We found a significant reduction in the number of days on total parenteral nutrition (P= 0.03) and a tendency to a reduction in the number of days on antibiotics (P= 0.06) in the io compared to the iv group. Bacteraemia did not occur in the io group, but was seen in 30% of the iv group (NS). The incidences of acute and chronic graft-versus-host disease, transplantation-related mortality, relapse and patient survival rates were similar in the three groups. Five patients examined with bone marrow scintigraphy showed the same distribution of granulocytes in the bone marrow directly after transplantation and 3 weeks after transplantation, whether the bone marrow was given by the io or by the iv route. We conclude that allogeneic bone marrow transplantation can safely be performed by io infusion, but haematopoietic recovery is not improved.