There is substantial progress in preventing and treating cytomegalovirus (CMV) infections and CMV-related disease after allogeneic bone marrow transplantation. In CMV-seronegative recipients, use of CMV-seronegative blood products eliminates most CMV infections. Effective prophylaxis for CMV-seropositive recipients is being studied. Preliminary results of controlled trials of prophylactic ganciclovir show reduced CMV-related interstitial pneumonia. Intravenous immunoglobulin (i.v.IG) may further reduce risk of interstitial pneumonia in both CMV-seronegative and -seropositive recipients by decreasing graft-versus-host disease. CMV infection is a lesser problem after autotransplant. Consequently, prophylaxis with CMV-screened blood products, i.v.IG, and antiviral drugs is not necessary. Treatment of CMV-related interstitial pneumonia remains problematic. Best results to date are with ganciclovir and high-dose i.v.IG.