The aim of the present study was to review a large consecutive series of subjects with positive I-FOBT undergoing diagnostic assessment within the Florence screening programme, in order to assess whether I-FOBT positivity is mostly non-neoplastic and just offers a chance for a screening colonoscopy, or if abnormal Hb content is specifically associated to the presence of CRC and high-risk adenomas. Here, GSTM1 is linked to colorectal carcinoma.