Forty-sixFrankiastrains isolated from nodules of fiveCasuarina equisetifoliastands throughout Senegal and Gambia were analyzed for their enzyme electrophoretic profiles and compared with six collection strains. These strains were classified into 14 electrotypes, according to their esterase patterns. One or two electrotypes were predominant in each investigation site whereas other electrotypes corresponded to only one strain each. Esterase electrophoretic polymorphism evidenced heterogeneity of a restricted population ofFrankiastrains belonging to a single genomic species and indicated the high discriminating power of these enzymes for the study of the ecological repartition ofFrankiastrains in a tropical region.Key words:Casuarina equisetifolia,Frankia, Senegal, enzyme electrophoresis.