A method was developed to grow Legionella pneumophila in continuous culture. A chemostat was used to simulate nutrient-limited, sub-maximal growth in the natural environmental and to provide a precisely-controlled growth regime. Cultures grew under forced aeration under conditions yielding up to 38% saturation of dissolved oxygen; supplemental CO2 (5%) at the same gas flow rates as ambient air had no effect on culture growth. Pleomorphiam was observed during growth under all conditions. Pigment was produced only at D < 0.03 h-1. Catalase was produced at higher growth rates, but not at higher temperatures. The pathogenicity was unaffected by altering either the growth rate or growth temperature.