Thirty Azospirillum strains were isolated from the rhizosphere of 13 maize (Zea mays L.) cultivars grown in 14 French soils, using a new specific method, which has been given the name ROSEA. Among these strains 26 were Azospirillum lipoferum and 4 were Azospirillum brasilense. Their characterization was achieved using biochemical tests and plasmid profiles. Biochemical patterns allowed clear differentiation between the two species. A large diversity in carbon source metabolism was found among the Azospirillum sp. strains regardless of their origin. The A. brasilense were much more closely related, and were found in only two of the rhizospheres studied. The 30 plasmid patterns were all different, and the plasmid-profiling technique can therefore be considered as strain specific. All the A. lipoferum harboured a 150-MDa plasmid, while all the A. brasilense harboured a 90 to 100-MDa plasmid. This result reinforces the hypothesis of the presence of such plasmids as an additional criterion for differentiating these two species. Key words: Zea mays, Azospirillum, ROSEA method, biochemical tests, plasmid profiles.