Fourteen of 23 female members of a church group experienced an acute self-limited illness characterized by chills, fever, chest pain, cough, and nausea, consistent with the diagnosis of Pontiac fever. All 14 affected women had used a whirlpool located in the women's locker room during a racquetball party. Legionella pneumophila serogroup 6 was isolated from the women's whirlpool. Nine of 14 cases showed a seroconversion to heat-fixed antigen prepared from the L pneumophila serogroup 6 isolate. Aerosol size studies show that the whirlpool aerator produced water droplets small enough to travel deep into the tracheobronchial tree but large enough to transport L pneumophila. This outbreak demonstrated that Pontiac fever may be associated with L pneumophila serogroup 6, that whirlpools can serve as a reservoir for these organisms, and that seroconversion can occur in the absence of illness.