and the Departments ofMathematics and Pathology.

Patients undergoing bronchoscopy for possible pneumocystis pneumonia were studied retro-spectively to characterize the impact of common viral pathogens on the course of advanced human immunodeficiency virus (HIV) disease and atypical pneumonia. In 327 episodes, Pneu-mocystis carinii was found in 220 (67%), cytomegalovirus (CMV) in 145 (44%), and herpes simplex virus in 16 (5%). Early deterioration in oxygenation and use of intensive care was less common in CMV-positive patients. Neither CMV nor P. carinii was a predictor of mortality in multivariate analyses. CMV was not associated with an increased prevalence of later CMV disease. Isolation of CMV from the bronchoalveolar lavage fluid of these patients was not an indication for antiviral therapy. Pulmonary shedding ofCMV may be associated with a decreased inflammatory response to P. carinii. The outcome of HIV-associated atypical pneumonia where no clear pulmonary pathogen is found on routine evaluation was no better than that of treated P. carinii pneumonia. Atypical pneumonias are the most frequent serious com-plication ofadvanced human immunodeficiency virus (HIV) disease [I). Of the identified causative agents, Pneumocysti