Abstract: A serological study of 282 serum samples collected from suspected patients with Legionnares' Disease was carried out in Beijing area during the period from Jan. 1994 to Aug. 1 995. It was shown that the positive rate of antibodies against all 1 4 serogroups of Legionella pneumophila was about 20% in 282 serological samples. However ,there was no significant differ- ence of positive rates among age groups ,sex groups as well as 4 seasons. In 58 positive cases ,Lp 12 was 36% ,Lp6 31% and Lp1 20% ,the rest was 13% respectively.