Chlamydia pneumoniae is a significant cause of both upper and lower respiratory tract infections. The spectrum of diseases ranges from asymptomatic infection to serious disease, including severe pneumonia and exacerbations of chronic bronchitis requiring mechanical ventilation, There is increasing evidence of involvement of C. pneumoniae infection in bronchial asthma, and the role of this agent in immunocompromised patients has also begun to be appreciated. Curr Opin Infect Dis 13:161-164. (C) 2000 Lippincott Williams & Wilkins.