Tularemia is a disease caused by Francisella tularensis and widely seen at northern hemisphere of the world. In Turkey, oropharyngeal infections caused by a less virulent serotype F.tularensis subsp. holarctica are more prevalent. The aim of this study was to present the results of an epidemiological research performed after the detection of tularemia cases from Biga county of Canakkale province, Turkey, in December 2009. Following the report of two tularemia suspected cases from two villages (Baliklicesme and Sinekci) of Biga, an epidemiological investigation was undertaken to inspect the situation in this area. Water samples, clinical samples as throat swabs, wound swabs and serum samples were collected. Samples were cultured on heart agar supplemented with sheep blood, cysteine and antibiotics. Cultures were incubated at 37 degrees C in 5% CO(2) and followed for 10 days. Suspected colonies were identified by slide agglutination test using F.tularensis antisera. F.tularensis antibodies were investigated by standard tube agglutination method. Positive results obtained with agglutination test were also checked for a probable cross-reaction with Brucella antibodies by Rose-Bengal test. Water and wound samples were investigated using real-time polymerase chain reaction (RT Taqman PCR; Quantica, Techne Inc, UK) with probe and primers specific for ISFtu2 gene. All of the cultures yielded negative results, however eight of 16 water samples, one lymph node aspirate and one throat sample were found positive in F.tularensis TaqMan RT-PCR test. In tube agglutination test positive antibody titers between 1:20-1:1280 were detected in 36 of 115 serum samples. Two cases with antibody titers of 1:1280 and accompanying acute clinical findings, were diagnosed as tularemia and treated accordingly. Lymphatic drainage fluid samples obtained from one of these patients yielded positive result in PCR, however clinical sample could not be obtained from the other patient. The only epidemiological linkage between these acute cases (n= 2) and the other seropositive subjects (n= 34) was the use of local water supply system. It was learned that water obtained through reverse osmosis system had been used as drinking water at Baliklicesme village. Pre- and post-reverse osmosis system water samples from Baliklicesme village and samples from water supply of Sinekci village revealed positive results for F.tularensis by PCR. Since the only epidemiological relation between these two villages was using local water supply, tularemia cases encountered in this area were attributed to a water-borne epidemic and an automatic chlorination system was set up at each water reservoir in these villages. The establishment of these preventive measures curbed the growth of the epidemic. The cases presenting with throat sore, fever, lymphadenopathy (more than 2 cm), non-responsive to beta-lactam antibiotics, should be further investigated for tularemia. This work emphasizes that systematic setup and control of water disinfection systems are crucial to prevent tularemia outbreaks. Community and related authorities should be educated about the importance of water sanitation and chlorination.