Molecular study of aerolysin and cytotonic enterotoxin genes by PCR and colony blot hybridization was performed in 117 strains of Aeromonas spp. isolated from different sources. Homogeneous distribution of these genes in A. hydrophila complex strains was observed. For A. caviae and A. sobria complex strains, aerolysin genes were more frequent than cytotonic enterotoxins genes. Of 64 A. caviae complex strains, only one (1.5%) amplified the 451 bp product for the aer gene, however, the same primers detected a 400 bp product in 50 (78%) strains. This product was sequenced and had two short regions with homology to several hemolysin genes. The genotype aer (+)/aerA(+)/hly (+)/ast (+)/alt (+) was detected in six A. hydrophila strains from food and environmental source. The most common genotype found in A. hydrophila strains was hly (+) (85%) and aerA(+) (78.7%), while in A. caviae complex strains was aerA(+) (32.8%). All A. veronii complex sobria strains were aer (+)/aerA(+). All A. caviae and A. hydrophila were positive when tested with aer probe using the colony blot test. Thirty-seven percent of A. hydrophila and 53% of A. caviae tested were positive for ast probe. Eighty-nine percent of samples were cytotoxic in Vero cells. Our data demonstrated that Aeromonas spp. can harbor and express virulence genes and reinforce the potential of Aeromonas as a human pathogen.