The objection to Staphylococcus var. aureus (Micrococcus pyogenes) as the etiologic agent of pseudomembranous enteritis stems from the observation that Staphylococcus has not been isolated in every case of the disease and from the assumption that the physical changes observed in the intestine are secondary to the associated shock. These objections are without foundation. S. aureus does not grow out on every culture medium. In a mixed flora it fails to grow out at all, unless the culture medium favors its growth and suppresses the competing micro-organism. Referring physicians have told me repeatedly that the stool cultures of their patients, desperately sick with pseudomembranous enterocolitis, did not grow out staphylococci. Upon culturing the stools of these patients on proper media the staphylococci grew out in dominant Proportions. The oral administration of staphylococci to monkeys, animals highly sensitive to the enterotoxin, does not make them sick and does not induce stools