We investigated prospectively cytomegalovirus (CMV) IgG antibody kinetics following infusion of a CMV hyperimmune globulin preparation in 19 consecutive patients undergoing allogeneic bone marrow transplantation (BMT). CMV IgG against late antigen was measured by enzyme-linked immunosorbent assay. On a prophylactic hyperimmune globulin regimen (100 mg/kg body weight every 20 days), the mean half-life (t1/2) +/- SD of CMV IgG in seronegative patients with seronegative marrow donors was 19.7 +/- 7.9 days after the first infusion on day -7 before BMT, 24.9 +/- 12.5 days after the second infusion on day +13 after BMT, and 19.4 +/- 6.9 days after the third infusion on day +33. The t1/2 in individual patients showed a wide variation ranging from 10.9 to 47.6 days. A therapeutic high-dose hyperimmune globulin regimen (200-400 mg/kg body weight at 4-day intervals) given to five patients resulted in high serum levels of CMV IgG, which were maintained throughout therapy, even in two patients with severe intestinal graft-versus-host disease. The variation of CMV IgG kinetics between individual BMT recipients may contribute to the lack of protection from active CMV infection observed in some patients.