Colorectal cancer is one of the most frequent and it prognosis is still serious. In France, diagnosis and screening applicated in numerous departements, and now in a path of generalization to the all country, is based on combination of searching blood into bowel movements (Haemoccult) for the screening of population with medium risk (age between 50 to 74 years old)and colonoscopy for the screening and diagnosis of pre-cancerous lesions for the patients with a high risk.Even if the efficiency of this strategy is proved, searching blood into the bowel movement by Haemoccult is still imperfect (a lot of false negative). Colonoscopy is not an ideal tool for screening. Indeed, its acceptability is not perfect and it constitute an invasive method, with complications, with a compulsory general anesthesia, implicating a high cost. The alternative of a screening method based on a non invasive method is required.