Specimens from 490 patients with suspected legionellosis from many parts of New Zealand were studied. Most of these were sera, but 36 specimens including material from lungs, pleural fluid and sputa were also examined. The sera were tested for the presence of antibodies to Legionella pneumophila serogroups 1 to 6 and Legionella micdadei. Serological evidence of legionellosis was found in 49 patients. Antibodies to L. pneumophila serogroup 6 predominated, while those to L. micdadei and L. pneumophila serogroup 1 were noted in smaller numbers. Antibodies to serogroups 2, 3, 4 and 5 of L. pneumophila were not often encountered.