Although infectious diarrheal disease of infants is one of the most common global disorders, the process of identification of the various pathogens and clarification of the pathogenesis of the disease has developed rather slowly. Certain enteric pathogens, such as salmonellae and shigellae, have been identified many decades ago. Far more difficult has been the elucidation of the role of seemingly "normal" inhabitants of the intestinal tract, notablyEscherichia coli, first described by the pediatrician Escherich. It was half a century ago that the German pediatrician Adam1suggested that special kinds ofE coli(the Dyspepsiecoli) were responsible for diarrheal disease of infants. Viewed from the vantage point of today, the techniques available to him were quite inadequate and merely measured a few biochemical activities of the strains. Nonetheless, his concept proved to be correct. Some years later, serologic studies disclosed that certain strains ofE colirecovered during epidemics