This article reviews the administration, efficacy, and safety of prophylactic intravenous immunoglobulin in patients with secondary immunodeficiency and those undergoing allogeneic bone marrow transplantation. Associated infections in these immunosuppressed patients are examined as they relate to transfusion-associated transmission, graft-versus-host disease, and other factors. In addition, the safety issues (including infection with cytomegalovirus and hepatitis C virus) involved in hematopoietic stem cell transplant patients given intravenous immunoglobulin are detailed by long-term follow-up of controlled clinical trials.