A total of 2,693 fecal specimens, with 1,422 from healthy persons and 1,271 from patients suffering from enteric diseases, was investigated to isolate species of the Morganella-Proteus-Providencia group and to evaluate the role of these bacteria in intestinal disorders. Most strains were isolated from two media, i.e., blood agar and tryptophan agar. Two of the species were more frequently found in diarrheal cases than in healthy controls. These species were Morganella morganii and Proteus mirabilis. Two new species of Enterobacteriaceae, i.e., Proteus penneri and Providencia rustigianii, were found in 33 and 5 people, respectively. However, these two species were not found more frequently in the diarrheal cases.