Examination of 200 samples from soil and the same number of samples from healthy human feces yielded 49 (24.5%) and 105 (52.5%) strains of heat-resistant Clostridium perfringens respectively. Fourteen (7.0%) strains isolated from soil and 37 (18.5%) from feces synthesized enterotoxin, as demonstrated by Tórtora's method, at sufficient levels to permit its detection by mouse lethality, microslide double gel diffusion or counterimmunoelectrophoresis tests, By using the Duncan-Strong (DS) method, only four (2%) enterotoxigenic strains from soil and 14 (7.0%) from feces were obtained. The supernatant fluid from two enterotoxigenic-negative strains grown in DS medium gave a false-positive reaction when they were injected intravenously into mice. Tórtora's medium was preferable because a larger number of isolated strains produced spores and enterotoxin to permit their recognition as enterotoxigenic strains.