Routine examination of the water system in an establishment where showers were used by staff after work or leisure activities revealed the presence of Legionella pneumophila. Descaling and steaming cleared the system but six months later recolonization was found to have occurred. L. pneumophila was isolated from air samples collected in the shower room whilst the shower was in operation. No clinical cases have occurred. Serological examination of those using the showers throughout the six month period together with a control group showed no evidence of infection.