Cytomegalovirus (CMV) interstitial pneumonia is a frequent and often fatal complication of allogeneic bone marrow transplantation. Because therapy for CMV pneumonia was, until recently, largely ineffective, prophylactic methods were explored. This study shows that the strategy of using CMV seronegative blood products for seronegative patients with seronegative donors or weekly administration of intravenous immunoglobulin for all other patients reduced the attack rate of CMV pneumonia. The results of this study are put into the perspective of previously published data.