BACKGROUND AND AIM:DIARRHEA IS ONE OF THE MOST PREVALENT DISEASES IN THE WORLD, ESPECIALLY IN DEVELOPING COUNTRIES. ONE OF THE MOST IMPORTANT CAUSATIVE AGENTS OF BACTERIAL DIARRHEA IS DIARRHEOGENIC ESCHERICHIA COLI WHICH CAUSES GASTROENTERITIS AND THIS GROUP INVOLVING ETEC, EPEC, EAEC, EHEC, EIEC, DAEC PATHOTYPES. THREE FIRST GROUPS AFFECTED SMALL INTESTINE AND THREE SECOND GROUPS AFFECTED COLON. THE AIM OF THIS STUDY IS TO IDENTIFY ETEC, EPEC, EAEC, EHEC, EIEC PATHOTYPES IN NORTH AND NORTH-WEST OF IRAN. METHODS:IN THIS STUDY FOR IDENTIFICATION OF E. COLI, SAMPLES WERE CULTURED ON MAC CONKEY AGAR MEDIA AND SUBSEQUENTLY BY BIOCHEMICAL TESTS: TSI, SIM, MRVP, SIMMONS CITRATE AND ALSO LACTOSE FERMENTATION, PRODUCTION OF ACID FROM SUGAR, PRODUCTION OF GAS AND H2S AND ALSO MOTILITY WERE EVALUATED. SAMPLES WITH E. COLI CHARACTERISTICS WERE SELECTED AND THEIR GENOMES WERE PURIFIED BY PHENOL-CHLOROFORM METHOD. AFTER EXTRACTION OF GENOMES, LT AND STA GENES IDENTIFIED BY PCR FOR ETEC, EAE GENE FOR ATYPICAL AND EAE AND BFP FOR TYPICAL EPEC, AA GENE FOR EAEC, STX1 AND STX2 AND EAE GENES FOR EHEC (STX1 OR STX2 OR BOTH FOR STEC) AND INVE FOR EIEC. RESULTS:FINALLY FROM 84 SAMPLES, 7.14% WERE ETEC, 4.76% EPEC, 1.19% EHEC AND 10.71% STEC. 64.28% WERE NONPATHOGENICE. COLI. NONE OF THE SAMPLES WERE POSITIVE FOR EAEC AND EIEC. CONCLUSION:ETEC, EPEC, EHEC AND STEC ARE IMPORTANT BACTERIAL AGENTS WHICH CAUSES DIARRHEA IN NORTH AND NORTH-WEST OF IRAN. COMPLEMENTARY STUDIES TO IDENTIFY PATHOTYPES IN OTHER PROVINCES CAN HELP TO ADOPT NECESSARY POLICIES AGAINST OUTBREAKS IN OUR COUNTRY