The clinical course of cytomegalovirus (CMV) pneumonia in seven consecutive bone marrow transplant (BMT) recipients during a 24-month period was studied. Retrospective analysis of clinical data on the recipients with CMV pneumonia during the illness and prospective follow-up of those who recovered from the pneumonia was performed. Those who had CMV as the sole pathogen and with lymphocytosis in the BAL or the peripheral blood during the illness recovered from the pneumonia. On the contrary, those who had mixed bacterial or fungal infection with peripheral lymphopenia died. Persistent lymphocytosis in the BAL and the peripheral blood, in the absence of CMV infection, was observed in the survivors. Two subsequently developed restrictive lung disease and two had relapse of their primary malignancy. These data suggest that CMV pneumonia in BMT patients is associated with significant long-term sequelae. The phenomenon of persistent lymphocytosis in the BAL and the peripheral blood, in the absence of CMV infection, supports Grundy's hypothesis that CMV pneumonia in BMT recipients is an immunopathologic condition.