Using a microagglutination test, the prevalence of antibodies against three species (10 groups) of Legionella was determined in 300 healthy donors, 120 non-pneumonic patients with immunodeficiency and 158 patients with pneumonia. The results showed that there were significant differences among all groups on positive rate and GMT in three groups. Lp6 was the highest, Lp1 and Lp8 came second. There were significant differences among three groups in positive rate and GMT to Lp1, Lp2, Lp6 and Lp8, in the group of patients with pneumonia was highest, the group of non-pneumonic patients with immunodeficiency was second and healthy group was the lowest. It was suggested that the infection with Lp6, Lp1, Lp8 was predominant in population in Dalian area. The latent infection, subclinical infection and legionella pneumonia in population might be existence simultaneously. Using test-tube agglutination, the paired sera collected from 74 pneumonic patients were studied, it was showed that 5.4% of admitted pneumonic patients was legionellosis.