Summary An attempt was made to evaluate the bacterial etiology of “summer diarrhea” in infants in Buenos Aires and surrounding areas, from January to March, 1961. Statistical study of 1092 observed cases indicated that the actual percentages (at the 95% reliability level) of enteropathogens in the population with gastrointestinal illness was within the following limits: Salmonella—10.3–14.2%; Shigella—1.4–3.1%; and enteropathogenic Escherichia coli—7.8–11.3%. S. typhimurium and S. newport were the prevalent Salmonella serotypes. Sh. sonnei and Sh. flexneri were the more frequently isolated Shigella serotypes. The majority of enteropathogenic E. coli strains were of the serological types 0111 and 055. In 20 cases two or more enteropathogens were simultaneously isolated. The nature of the pathogenic flora did not appear to be significantly related to the trophic state. However, Shigella was more frequently found in the more severely dystrophic infants. It was also more frequently found in the severe cases of diarrhea and in the 12–15 month age group.