In order to develop a scoring system for selecting patients at high risk of organic diseases of the colon, who would need a colonoscopy or a barium enema, we conducted a study with 14 GPs in the local health care district of Modena. Over one year, 254 consecutive patients who consulted their GP for chronic abdominal pain were asked to answer a guided questionnaire. A checklist of simple parameters suggestive of the presence of organic diseases of the colon was also registered by the GP. For the final diagnosis, the patients underwent either a colonoscopy or a barium enema. Data collected were analysed by means of a stepwise logistic regression analysis to obtain a weighted score for the diagnosis of either irritable bowel syndrome (score less than 0) or organic disease (score greater than 0). Out of the 25 parameters explored, six were significantly more common among patients with organic disease and weighted as positive score (namely ESR greater than 17 mm, first hour, history of blood in the stool, leukocytosis greater than 10,000 cm3, age greater than 45 years, slight fever and presence of neoplastic colonic diseases in first-degree relatives). On the contrary, five parameters were more frequent among patients with irritable bowel syndrome and weighted as negative score (namely visible distension of the abdomen, feeling of distension, presence of irritable bowel syndrome in first degree relatives, flatulence and irregularities of bowel movement). Our scoring system correctly classified 83.5% of the cases, and it was very sensitive (82.4%) for the diagnosis of organic disease.(ABSTRACT TRUNCATED AT 250 WORDS)