A series of 737 hemodialysis patients were studied for the relationship between lymphocytotoxic antibody formation and blood transfusions; 331 thereof were studied prospectively. With up to 20 transfusions, highly reactive (greater than 90% reactivity against random panel) antibodies were not found in any of the prospectively studied males or females without previous pregnancies. Nearly 90% of the males failed to form antibodies against greater than 10% of the panel donors. Patients with previous pregnancies developed antibodies at a much higher rate. Among 316 patients tested, antibodies against B cells were found more frequently than antibodies against T cells. Both T and B cell antibody levels often decreased in spite of additional transfusions. It is concluded that the risk of rendering a patient untransplantable because of sensitization as a result of transfusions is very small.