Comparative analyses were performed at the immunological, biological, and genetic level to establish the degree of relatedness of a group of four cytotoxic enterotoxins and aerolysins produced by different isolates of Aeromonas: SSU [16], Ah1 [13], Ah2 [18], and Ah65 [21]. Results obtained from Western blot analysis, neutralization studies, and Southern blot analysis indicated that although the members of this group of toxins displayed structural similarities they also differed from each other at the immunological, biological and genetic level.