Background: Enterohemorrhagic Escherichia coli (EHEC) is one of diarrheagenic E.coli that produce Shiga toxins (Stx) causing diarrhea, Hemorrhagic Colitis (HC), and Hemolytic Uremic Syndrome (HUS). E. coli O157:H7 is the most common and the one that can be identified in the clinical specimens of the EHEC species. Shigella dysenteriae type 1(Shigella shiga) produces shiga toxin, identical to Stx-1, thus causes HC and HUS. Aim: the aim of this work was to detect the role of Shigella shiga and E. coli O157 as causative agents of hemorrhagic diarrhea, and detecting cytopathic effect of verotoxin producing E. coli O157 on tissue culture. Material and Methods: 70 stool samples collected from patients with bloody diarrhea were investigated for the presence of E. coli O157 and Shigella shiga by culture methods on Sorbitol MacConkey agar and ChromIDTM O157:H7) and latex agglutination test. Cytotoxic effect to Vero cells of isolated E. coli O157 was also determined. Results: this study found that (10%) of isolated organisms was E.coli O157, Shigella shiga also represent the same percent, while E.coli O111 and E.coli O26 represent (8.6%, 5.6%) respectively. About 85.7 % of isolated E.coli O157 showed a reasonable toxicity to Vero cells post treatment with bacterial toxin by tetrazolium-based colorimetric assay (MTT assay). Conclusion: E. coli O157 and Shigella shiga play major role in the etiology of hemorrhagic diarrhea. In addition, stool culture on Sorbitol MacConkey agar followed by ChromIDTM O157:H7 agar is a simple and reliable method for E. coli O157 detection.