Legionella pneumophila has frequently been isolated from patients with Legionnaires disease and in several instances also from epidemic-related environmental samples. A selective medium was developed and used successfully to isolate Legionella pneumophila and Legionella-like organisms from environmental specimens animal inoculation methods. Legionella pneumophila is a Gram-negative, facultative, intracellular bacterium that is the causative agent of Legionnaires' disease. This medium consists of charcoalyeast extract agar to which have been added cephalothin (4µg/mL), colistin (16µg/mL), vancomycin (0.5µg/mL), and cycloheximide (80µg/mL). Pretreating of the environmental water samples with an acid buffer (pH 2.2), followed by plating on the selective medium, improved the rate of recovery of both Legionella and Legionella-like organisms relative to that with direct plating on selective media.