A 22-year-old man who underwent syngeneic bone marrow transplantation (BMT) for acute lymphoblastic leukemia acquired a human immunodeficiency virus (HIV) infection by transfusion of blood products from a donor at risk. The manifestations were acute encephalopathy together with immune thrombocytopenia in the early posttransplant period, and acquired immunodeficiency syndrome (AIDS) developed 20 months after BMT. Because he had a syngeneic donor, the possibility of reconstituting the immune system was investigated by repeated transfer of healthy syngeneic lymphocytes and by combining repeated transfer of syngeneic lymphocytes with the antiviral agent suramin to protect the infused leukocytes from being attacked by HIV. No improvement was observed clinically or in the patient's immune functions by these efforts.