Total DNA of various Azospirillum strains representing different species was digested with restriction enzymes, Southern blotted and hybridized with four A. brasilense probes. Pairwise comparison of the conserved hybridization fragments was applied to calculate sequence divergence and to group the strains using the unweighted pair group method. The resulting dendrogram grouped the strains according to the known species indicating that the analysis of the restriction fragment length polymorphism is an useful tool for characterizing Azospirillum isolates