Until the outbreak of the Chicago epidemic in 1933 amebiasis was believed to be encountered only in the tropics. The Chicago outbreak, however, called attention to amebiasis as a worldwide disease. Recent surveys with much improved laboratory methods, such as the use of polyvinyl alcohol preservative, hematoxylin-stained slides, Faust's flotation for cysts and culture of amebas show that approximately 20 per cent of the population of the United States is infested. Craig, Faust, D'Antoni and others have shown that most of the persons infected with Endameba histolytica do not present a textbook picture of amebiasis but suffer from a subclinical form of the disease or have chronic constipation alternating with short outbursts of diarrhea. Such patients usually seek medical aid for symptomatic disturbances. According to the situation of the main lesions, the symptoms may be localized in the appendiceal region, the hepatic flexure, the splenic flexure or the descending colon.