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With the aim to evaluate the salt stress tolerance of 12 cowpea (Vigna unguiculata L. Walp.) varieties by using some variables relative to nodule formation, aerial dry mass and its nitrogen content, two simultaneous experiences in saline and not saline soils were carried out. A completely randomize block design with three repetitions was used in both experiences. The aerial and roots dry mass, number of nodules per plants, number of effective nodules, nodules dry mass and nitrogen content in aerial mass were evaluated at 40 days after sowing. Using the measured results the tolerance index to salinity in all varieties was calculated, which were classified using a Cluster analysis of Complete Linkage, based on Euclidian distance. The results evidenced the affectation of all varieties sowed on saline soil when the nodules number, its dry mass, as well as the aerial dry mass and its nitrogen content were evaluated, but the main differences among genotypes, and the tendency to saline tolerance were found by using the cluster analysis, through which varieties were classified in two different groups. Into the first group, eight genotypes with marked tolerance characteristic to saline stress were located, while the others four varieties were categorized as susceptible, being situated into the second group. [ABSTRACT FROM AUTHOR]