Between May 1987 and September 1989, 72 patients undergoing marrow transplantation at a single institution were randomized to receive 50 mg/kg of a commercial gammaglobulin preparation or placebo daily in four divided doses for 28 days following transplantation. Patients receiving oral gammaglobulin had significantly increased concentrations of stool IgG (p = 0.01) compared with the placebo group. There was no difference in the amount of diarrhea, frequency of GVHD, duration of hospitalization or survival in the two groups. The present study demonstrates that orally administered IgG can survive passage through the gastrointestinal tract of bone marrow transplantation recipients but there was no effect of oral administration of immunoglobulin on morbidity or mortality following bone marrow transplantation.