During the period from December 1989 to January 1990, An outbreak of upper respiratory infection (influenza-like syndrome) took place in the workers of a building-site in a rural area of Beijing. An epidemiological investigation and bacteriological examination were carried out in this area. The results showed that it was an outbreak of Legionnaires' Disease caused by Legionella micdadei (Lm). The incidence was 26.67% (24/90). This was the first report on Lm infection in China.