Distribution of Legionella species over Japan was investigated.Five hundred ml of various environmental sources (343 samples of cooling tower water, 25 samples of water of puddy field. 29 samples of river, 3 samples of lake, 1 sample of fountain, 2 samples of puddle, 4 samples of well water, 6 samples of hemodialysate, 5 samples of antiseptic solution for washing hands at operating room) were cultured for isolation of Legionella spp.Isolations of the organism were applied to intraperitoneal injection to guinea pigs and direct inoculation to semiselective medium (B-CYE agar with antibiotics) after low pH treatment.One hundred sixty-six strains of Legionella spp. were isolated from 126 (36.7%) out of 343 cooling tower water samples.The origin of positive samples ranged from Hokkaido (Northern Japan) to Okinawa (Southern Japan).L. pneumophila, serogroup 1 was the most frequent isolates (66.3%); next in frequency of occurrence were Legionella-like organisms (16.3%), L. pneumophila serogroup 4 (7.2%), L. bozemanii (7.2%), L. pneumophila serogroup 6 (1.8%) and serogroup 3 (1.2%).L. pneumophila serogroup 2, serogroup 5, L. micdadei, L. dumoffii, L. gormanii, L. longbeachae and L. jordanis were not isolated from cooling tower water samples in this study.Five out of 28 soil samples were positive culture of Legionella spp. with L. pneumophila serogroup 1 (5 strains), serogroup 4 (2 strains) and serogroup 5 (1 strain).One strain of L. pneumophila serogroup 1 was isolated from one of 2 samples of puddle in construction sites. No positive culture was obtained from remaining materials.These results indicated that many types of Legionella species were widespread in all over the country.Environmental isolates possessed to have almost same endotoxin-like activity as clinical isolates by limulus test. However, there was some variations in virulence to mice among environmental isolates.