Abstract A comparison was made between 65 strains of root nodule bacteria from indigenous New Zealand legumes and 45 reference strains including: Rhizobium trifolii, R. phaseoli, R. leguminosarum, R. meliloti, and both “acid-producing” and “non-acid-producing” strains from the Lotus-Lupinus-Ornithopus cross-inoculation group. The strains were classified into 10 clusters on the basis of 37 morphological, cultural, and physiological tests. Relationships disclosed among the reference strains were in accordance with current ideas on Rhizobium taxonomy. The indigenous strains were well separated from both the trifolii-leguminosarumphaseoli complex and R. meliloti but acid-producing strains from the Lotus-Lupinus-Ornithopus cross-inoculation group segregated with the indigenous strains. The principal characters differentiating the clusters are discussed. The base composition of DNA from representative indigenous strains was determined and base sequence homology studied. The relative reassociation at 65°c in 0.2...