Interstitial pneumonitis due to cytomegalovirus is a major cause of morbidity and mortality in severely immunocompromised patients, particularly those who have had allogeneic bone marrow or solid organ transplantation, or who have the acquired immunodeficiency syndrome (AIDS). The mortality rate for cytomegalovirus pneumonia after marrow transplantation has been extremely high (>85%) in most studies reported, despite the use of various antiviral drugs and immunotherapeutic agents. Although ganciclovir (9-1,3 dihydroxy-2-propoxymethylguanine) has been reported to have excellent antiviral activity in vivo, when it is used alone or in combination with high-dose corticosteroids, it has had little impact on the overall survival of patients with cytomegalovirus pneumonia after allogeneic marrow transplantation. Similarly, therapy with intravenous cytomegalovirus immune globulin alone did not improve survival. After a preliminary report from the Medical College of Wisconsin, we studied the effectiveness of combined treatment with high-dose intravenous immune globulin and ganciclovir for cytomegalovirus pneumonia after allogeneic marrow transplantation. Because of the success of this regimen and its impact on survival, we report the clinical, serologic, and virologic results in the initial ten patients treated.