Seventy one patients underwent bone marrow transplantation for aplastic anaemia or haematological malignancy, 39 as allografts and 32 as autografts. All patients who were seronegative to cytomegalovirus received blood product support exclusively from seronegative community blood donors; seropositive patients received unscreened products. In no patients was there any attempt to reduce cytomegalovirus (CMV) infection by giving prophylaxis with immunoglobulin, and granulocyte transfusions were not given. The incidence of cytomegalovirus infection in the seronegative recipients (22 allograft, 15 autograft) was 0%; in the seropositive recipients 16 (63%) in allografts and 17 (18%) in autografts. These results suggest that provision of exclusively seronegative blood products is an important contribution for seronegative transplant recipients, but make little impact in autologous transplantation where the incidence of infection is low.