Intravenous immunoglobulin has been used after bone marrow transplants to prevent infections and acute graft-versus-host disease. However, the minimum dose required for protection is unknown. This may have significant economic implications. A multicenter randomized clinical trial compared the impact of two intravenous immunoglobulin doses on systemic infections and acute graft-versus-host disease in transplant recipients. Either 250 mg/kg or 500 mg/kg was given weekly from day -8 to day +111. Multivariate analysis was used to assess the effect of dose and other risk factors on event-free survival, systemic infection, and acute graft-versus-host disease. The two-dose cohorts had similar event-free survival and infection frequencies. The higher dose was associated with less acute graft-versus-host disease (P = 0.03).