In ten patients, amebic colitis was mistakenly diagnosed as ulcerative colitis or Crohn disease of the colon because of the similarity of history, physical examination, and routine laboratory studies as well as findings on proctoscopic and barium enema examination. Multiple stool examinations failed to demonstrate ova or trophozoites of Entamoeba histolytica. Routine examinations of stools for ova and parasites are inadequate and even a meticulous search for amebas in fresh stool, in scrapings from bowel ulcer, or in biopsy material may give negative results. The indirect hemagglutination test was shown to be a reliable diagnostic test in the evaluation of these cases. Because corticosteroid treatment of patients with amebic colitis may lead to undesirable complications the indirect hemagglutination test results should be obtained in patients in whom such diagnostic confusion is likely.