SummaryEighty of 103 strains of Aeromonas hydrophila cultured at 100 rev./min produced heat‐labile enterotoxins detected using the suckling mouse assay. Results in intestinal perfusion agreed with the suckling mouse test in all strains tested by both methods. Enterotoxic activity correlated with haemolysin and cytotoxin production, but 4% of strains would have been wrongly classified using haemolysin assay in place of the suckling mouse test and 11% misclassified on the basis of cytotoxin assay. There was a significant association between haemolytic and cytotoxic activity, but 15% of strains produced only one of these toxins. Haemolysin, cytotoxin and enterotoxin were not always associated in a given isolate. The time of appearance of exotoxins during bacterial growth and the effects of dialysis, hearing and proteolytic enzymes also suggest that haemolysins, cytotoxin and enterotoxins of Aeromonas hydrophila are separate toxins and not different manifestations of the same toxin.