Cytomegalovirus (CMV)-specific immunoglobulin (IVIG) was evaluated in a randomized controlled trial in CMV-seronegative marrow transplant patients with seropositive marrow donors for the prevention of primary CMV infection during the first 100 days after transplant. Patients received 200 mg/kg CMV IVIG on days 8 and 6 before transplant, the day after transplant, weekly for the first month, and then every 2 weeks to complete 10 doses. Patients were followed with weekly CMV cultures and serologic studies and for clinical and histologic evidence of CMV disease. Sixty patients were evaluable in each group. There was significantly less CMV excretion (P = .04) and viremia (P = .01) in the treatment group. However, the incidence of CMV disease including CMV pneumonia, CMV enteritis, and CMV syndrome (fever, leukopenia, hepatitis) was not statistically different. There was also no difference in median time of onset of CMV infection or disease, median number of hospital days, or survival between the two groups.