Several transfusion-related complications have particular relevance to the transplant setting. Transfusions reportedly improve solid organ graft survival, especially when the donor and recipient share at least one HLA-DR antigen. Whereas the mechanism for this effect is unclear, less favorable "immunomodulating" effects of transfusion may increase postoperative infections and shorten survival time and disease-free intervals in patients with a variety of malignancies who are undergoing surgery. The contribution of the different components of the blood transfusion to these outcomes remains speculative. Directed donations, especially from relatives and in the setting of a recipient who is immunosuppressed, may give rise to a severe but under-appreciated immunologic consequence of transfusion: graft-versus-host disease. Although still rarely reported, transfusional graft-versus-host disease is almost invariably fatal. This complication is entirely avoidable if the transfused blood product is appropriately gamma-irradiated. Infectious complications remain the most feared consequence of transfusion; the cytomegalovirus, the human immunodeficiency virus, and hepatitis B and C may run a more fulminant course in transplant patients who are immunosuppressed. Red cell substitutes, hematopoietic growth factors, and autologous transfusion are among the strategies for preventing complications of blood transfusion. With the advent of cyclosporine and more potent and specific immunosuppressive therapies, the desirability of preoperative transfusion for organ grafts warrants reevaluation.