Cytomegalovirus infections in bone marrow transplant recipients given intensive cytoreductive therapy. Cytomegalovirus (CMV) infections were studied in 785 bone marrow transplant recipients given intensive cytoreductive therapy. CMV excretion occurred in 24%, viremia in 9%, seroconversion in 40%, and overall active infection in 47%. CMV disease was much less common. Retinitis, enteritis, and pneumonitis occurred in only one, five (less than 1%), and 55 (7%) of the patients, respectively. Allograft recipients were more likely to develop CMV disease than were autograft patients (P = .0001) despite comparable rates of active CMV infection. CMV disease was rare after primary infection in both autograft and allograft recipients (0 and 1%, respectively). In contrast, CMV disease occurred in 16% of seropositive allograft recipients. Among allograft recipients, risk factors for CMV pneumonitis were seropositivity, age greater than 10 years, and acute graft-vs.-host disease, while the use of cyclosporine as prophylaxis against graft-vs.-host disease was protective. Although active infection rates did not decrease, the rates of CMV pneumonitis in allograft recipients during successive years declined significantly (P less than .001). 