Two cases of amebic colitis that resulted in perforation of the colon, an ominous complication, are presented. The first was diagnosed preoperatively as acute ulcerative colitis with toxic megacolon, and the second as peritonitis complicating acute cholecystitis. In both instances the correct diagnosis was made after operation. The first patient recovered after colectomy and antiamebic therapy, but the second patient died in the early postoperative period, in septic shock. Amebic colitis occurs infrequently in the United States, and the diagnosis is rarely considered. In most cases an initial diagnosis of ulcerative or granulomatous colitis is made and the true diagnosis is recognized only after operation for colonic perforation or hepatic abscess. It is suggested that amebic colitis should be considered more frequently in cases of patients who have diarrhea. Stool examination for ova and parasites is often negative in amebic colitis. The IHA is usually positive in emebiasis, and should be performed early in casesof patients who have bloody diarrhea or other clinical symptons when amebiasis is suspected. Rectal biopsy is also a useful diagnostic approach, but failed to reveal amebae in one of our cases. Finally, it is suggested that operation be performed urgently when fulminating amebic colitis is not reversed by antiamebic therapy, when peritonitis occurs even with antiamebic treatment in progess, and for colonic perforation or toxic megacolon even when antiamebic therapy has not been indicated.