There is increasing evidence that screening for colorectal cancer may save lives, and consequently, both professional and public interest in screening for colorectal cancer is increasing. As yet, however, there is no perfect screening test. Insidious blood loss is a common feature of colorectal cancer and may lead to a fall in serum ferritin before the patient becomes anemic. Measurement of serum ferritin, which is widely available and easily and inexpensively performed, has, therefore, been postulated as a potential screening test for colorectal cancer.This study used samples of serum collected from 148 patients recruited to a screening study for colorectal cancer. All patients were thoroughly investigated by double-contrast barium enema and/or colonoscopy. Patients were selected randomly from each of three clinical diagnostic groups: 50 patients with proven colorectal cancer, 49 patients without colon disease, and patients with adenomas of the colon. Serum ferritin was assayed by immunoradiometry. The expected adult reference ranged is 25 to 350 milligrams, and results were reported without patient identification.There were no significant differences in serum ferritin levels among any of the three groups.Serum ferritin is unlikely to be of value as a screening test for colorectal cancer.