A total of 249 strains of mesophilic Aeromonas including 179 A. hydrophila and 70 A. caviae were tested for production of cholera-like enterotoxin by reversed passive latex agglutination (RPLA) assay. A cholera-like enterotoxin neutralized with cholera antitoxin was demonstrated in the culture filtrates from eight (4.5%) of the 179 A. hydrophila strains, while none of A. caviae strains revealed the enterotoxin production in the test. Production of the cholera-like enterotoxin in the eight strains of A. hydrophila was also confirmed by enzyme-linked immunosorbent assay (ELISA).