This article reviews the clinical symptoms of legionnaires' disease, describes the natural and man-made habitats of Legionella pneumophila, and evaluates various disinfection methods. Although heat rejection devices (cooling towers and evaporative condensers) have been linked to outbreaks of legionnaires' disease, recent evidence suggests that potable water distribution systems are the primary reservoirs of L. pneumophila. Inhalation of aerosols containing the organism, instillation of the organism into the lung via medical maneuvers of the respiratory tract, and aspiration of contaminated water into the lung are the most likely modes of transmission of L. pneumophila. Treatment methodologies include hyperchlorination, thermal eradication, ozonation, and ultraviolet light irradiation. Includes 72 references, figures.