A series of O:H serotypes of E. coli were incriminated by epidemiologic studies in the period 1945-1960 as a cause of epidemic diarrhea in infant nurseries as well as a major cause of sporadic infant diarrhea in the community. The term enteropathogenic E. coli was coined to refer to these infant diarrhea-associated serotypes. In the early 1970s, with the advent of laboratory tests to assess heat-labile and heat-stable enterotoxin production and enteroinvasiveness of E. coli, the classic serotype enteropathogenic E. coli strains were found to lack those particular properties. These observations led some to question their pathogenicity. However, since 1978, enteropathogenic E. coli have come to be appreciated anew as a separate class of diarrheagenic E. coli that cause diarrhea by distinct pathogenic mechanisms. The pathogenesis of these strains, which have been shown to cause diarrhea in volunteers, appears to involve both an enteroadhesiveness step and production of a toxin identical to Shigella toxin. A 55- to 65-Mdalton plasmid is involved in the attachment of enteropathogenic E. coli to intestinal mucosa which results in a pathognomonic histopathologic lesion visualized by electron microscopy. The lesion involves dissolution of enterocyte microvilli by the bacteria, effacement of the enterocyte outer membrane, and formation of a pedestal around the bacterium at point of contact with the outer membrane of the enterocyte. Case-control epidemiologic studies carried out since 1975 document that enteropathogenic E. coli remain an important cause of sporadic infant diarrhea in the community with up to 30 per cent of cases of acute diarrhea in young infants in Brazil and South Africa being attributed to these pathogens. Although nursery epidemics of enteropathogenic E. coli diarrhea have virtually disappeared from industrialized countries, some sporadic enteropathogenic E. coli diarrhea in infants in the community continues to occur. The relative importance of enteropathogenic E. coli as a cause of sporadic diarrhea in both industrialized and developing countries needs to be reassessed. New diagnostic techniques are awaited to simplify this task.