An etiological study of bacterial diarrhea in infants under five years of age in Paraguay from May to July of 1990 was done. Enteropathogenic E. coli (EPEC) strains of known serogroups were isolated from 35.8% of the patients with diarrhea, Salmonella spp. were isolated from 15.1%, enterotoxigenic E. coli (ETEC) strains were isolated from 5.7%, and Shigella and Campylobacter spp. were isolated from 3.8% respectivery. No enteroinvasive E. coli (EIEC) or Vibrio spp. was isolated. Out of 53 diarrheal patients, 34 cases (64.1%) had bacterial diarrheal diseases. The infants under one year of age with diarrhea were predominant among inpatient and outpatient children under five years of age and the total number of male diarrheal cases was greater than that of female cases. Enteropathogenic organisms were isolated from nine out of 12 water samples taken from the Paraguay River. The major serotype (018) of the EPEC isolated from the water samples of the Paraguay River corresponded to the major serotype isolated from patients with diarrhea.