A selective medium was developed and used successfully to isolate Legionella pneumophila and Legionella-like organisms from environmental specimens previously positive by animal inoculation methods. This medium consists of charcoal-yeast extract agar to which have been added cephalothin (4 micrograms/ml), colistin (16 micrograms/ml), vancomycin (0.5 microgram/ml), and cycloheximide (80 micrograms/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.