Following ablative treatment with supralethal doses of chemotherapy and total body irradiation, patients demonstrate multiple immunologic deficiencies after bone marrow transplantation. Immune function usually recovers and the risk of infection decreases within six to 12 months. However, patients in whom chronic graft-versus-host disease (GVHD) develops have persisting B and T cell abnormalities, and in vivo and in vitro studies show impaired immunoglobulin regulation and function despite normal levels of serum immunoglobulin G. This review summarizes 12 published clinical trials of immunoglobulin therapy to correct immunodeficiency and prevent infection after marrow grafting. In five controlled studies, cytomegalovirus infection developed in a total of 52 of 172 (30 percent) immunoglobulin recipients and 71 of 165 (43 percent) control patients not given globulin. In four controlled trials, interstitial pneumonia developed in a total of 21 of 127 (17 percent) immunoglobulin recipients and 40 of 94 (43 percent) control patients. Three randomized trials reported a reduced rate of GVHD or post-engraftment septicemia in immunoglobulin recipients. However, methods of immunoglobulin preparation, antibody titer, and dose and schedule of prophylaxis varied widely in these studies, as did other critical patient, transplant regimen, and supportive care factors. Accordingly, data should be interpreted with caution. Ongoing controlled clinical trials will further define the proper role of immunoglobulin therapy in bone marrow transplantation.