Twenty-one patients with Fanconi's anaemia (FA) were treated by allogeneic bone marrow transplantation (BMT). Two, transplanted before 1980, received high dose cyclophosphamide conditioning and both died. Subsequently 19 patients received conditioning with low dose cyclophosphamide 5 mg/kg x 4 and total body irradiation 200 cGy x 3. Ten of 19 received HLA identical sibling marrow (ID-BMT) and nine marrow from alternative donors (MM-BMT). Marrow was T cell depleted in 9/19 cases. Sustained engraftment was observed in 13 cases (eight ID-BMT, five MM-BMT). Nine patients developed greater than or equal to grade II acute graft-versus-host disease (GVHD) (six ID-BMT, nine MM-BMT). Chronic GVHD occurred in 5/11 evaluable patients. Overall survival of the low dose cyclophosphamide group was 9/19 (47%) at a median follow-up of 1257 days post-BMT (110-1825). Six of 10 (60%) survived after ID-BMT compared with two of nine (22%) after MM-BMT. We conclude that allogeneic BMT using a low dose cyclophosphamide protocol is a satisfactory treatment for FA patients who have a normal HLA identical sibling. The results of MM-BMT have been poor, and must improve before these transplants can be generally recommended for treatment of FA.