Laboratory investigations supported the diagnosis of legionella pneumonia in 108 patients in South Australia over the past 10 years. Legionella pneumophila was responsible for 91 infections: the serogroup-1 strain caused 81 of these. L. pneumophila serogroup 2 was the only other strain of L. pneumophila that was isolated from patients; it caused infection in eight patients. In two patients, the serological results did not distinguish between infection with L. pneumophila serogroup 1 and serogroup 2. Legionella longbeachae serogroup 1 accounted for the remaining 17 infections. Serological tests were used to make the diagnoses in 77 cases. Legionella spp. were isolated from 24 patients and were identified in the respiratory-tract secretions of a further seven cases by direct immunofluorescence microscopy. L. longbeachae serogroup 1 first was isolated from a patient with pneumonia in South Australia in May, 1987. Since then it has been isolated from specimens from six other patients. No evidence exists for a common-source outbreak of L. longbeachae but an outbreak of Legionnaires' disease that was caused by L. pneumophila serogroup 1 occurred in South Australia in 1986.