Two Legionella-like organisms were isolated from water samples obtained in Adelaide, Australia. One organisms was isolated from a drinking water distribution system, and the other was isolated from a cooling tower at a sewage treatment plant. Both strains required L-cysteine for growth and contained cellular branched-chain fatty acids and ubiquinones typical of the genus Legionella. These strains were serologically distinct from each other as determined by a slide agglutination test. STrain 2074-AUS-ET (T = type strain) was serologically distinct from all previously described Legionella species and serotypes. Strain 2055-AUS-E could not be differentiated biochemically or serologically from Legionella quinlivanii. Both strains were shown by DNA hybridization studies (Hydroxyapatite method) to be members of new Legionella species. Legionella waltersii sp. nov. is the name proposed for strain 2074-AUS-ET (= ATCC 51914T). L. waltersii was less than 10% related to other Legionella species. Strain 2055-AUS-E (= ATCC 51913) was informally named Legionella genomospecies 1, since it could not be phenotypically distinguished from L. quinlivanii. Legionella genomospecies 1 was closely related to L. quinlivanii strains (53 to 69% related with 4.5 to 6.5% divergence at 60 degrees C and 31 to 52% related at 75 degrees C).