In many countries of the world, Escherichia coli 0157:H7 has been detected as a causative agent in cases with gastroenteritis. There is limited number of studies conducted with E. coliO157:H7 in Turkey. In the present study, we investigated the bacterium in 200 patients with bloody stool as well as in 50 unpasteurized milk samples using ideal isolation techniques. Stool and milk samples were inoculated into the Sorbitol MacConkey Agar, which is selective for E.coli 0157:H7 and in other mediums. E.coli strains unable to ferment sorbitol were exposed to agglutination using the anti–serum prepared against O antigen. E.coli 0157:H7was not detected either in 200 patients or 50 milk samples. EnterohemorrhagicE.coli serotype 0157:H7 is not a common bacterium in Turkey. Exploration of this agent, which is found in other countries, should not be neglected particularly in patients with gastroenteritis with a history of bloody stool or eating suspicious foods.