The main objective of the present work is to estimate the variability of salinity tolerance of five varieties of cultivated alfalfa (Medicago sativa L.). This was done in order to develop a classification of tolerance thresholds to salinity stress, an important criterion in the choice of varieties to be retained in a development program in areas affected by salinity. The study was carried out on the one hand at the germination stage and on the other hand at the first stages of growth. For the germination stage we evaluated the effect of different concentrations of NaCl on the germination rate. For the seedling stage, the effect of salt stress was studied on a number of agro-morphological traits under controlled conditions.