Amebiasis is an infection of the large intestine produced by the protozoan Entamoeba kistolytica . The disease occurs worldwide but is most prevalent in South and West Africa, Southeast Asia, Mexico, and the western part of Latin America.' More than 10% of the world's population is estimated to be infected. E kistolytica is the third leading parasitic cause of death in developing nations, after malaria and schistosomiasis. In the United States, the prevalence has declined from 5% to 10% in 1960 to approximately 1% to 4% currently. However, amebiasis is one of the most important pathogens to which travelers to endemic countries are exposed. Other groups also are at higher risk of acquiring E kistolytica infection. Sixteen percent to 32% of homosexual men have been found to have E kistolytica in stool specimens. E kistolytica also has been reported as an occupational disease in flight personnel working for commercial airlines.” Because humans are virtually the exclusive reservoir of E kistolytica , appropriate control measures could result in a substantial reduction in the incidence of the disease. Entamoeba has seven species including Entamoeba hartmanni, Entamoeba coli, Entamoeba colecki , and Entamoeba gingivalis ; only E kistolytica causes disease in humans. The morphologic classification of Entamoeba is based on the number of nuclei in the mature cyst.' E kistolytica is further characterized by its unique antigens, DNA characteristics, and isoenzyme analyses. In contrast to the free-living amoeba, E kistolytica requires the presence of either bacteria or tissue substrates to satisfy its nutritional needs. It can be cultivated on artificial media, but the diagnostic value of culture remains uncertain.