Persistent symptoms of constipation, such as straining, hard stools, sensation of incomplete evacuation, sensation of anorectal obstruction, manual manoeuvres to facilitate defecation, and infrequent defecation are diagnostic criteria identifying patients with functional constipation, 1 Thompson W.G. Longstreth G.F. Drossman D.A. et al. Functional bowel disorders and functional abdominal pain. Gut. 1999; 45: II43-II47 Crossref PubMed Scopus (2010) Google Scholar but symptoms alone do not enable a distinction between constipation due to slow transit and cases due to obstructive defecation. Nor do they identify patients who complain of constipation but have a normal transit and pelvic floor function. 2 Rao S.S. Ozturk R. Laine L. Clinical utility of diagnostic tests for constipation in adults: a systematic review. Am J Gastroenterol. 2005; 100: 1605-1615 Crossref PubMed Scopus (209) Google Scholar Various function tests are used today to assess functional constipation states, including scintigraphy, 3 van der Sijp J.R. Kamm M.A. Nightingale J.M. et al. Radioisotope determination of regional colonic transit in severe constipation: comparison with radio opaque markers. Gut. 1993; 34: 402-408 Crossref PubMed Scopus (104) Google Scholar , 4 Cremonini F. Mullan B.P. Camilleri M. et al. Performance characteristics of scintigraphic transit measurements for studies of experimental therapies. Aliment Pharmacol Ther. 2002; 16: 1781-1790 Crossref PubMed Scopus (164) Google Scholar fluoroscopy and magnetic resonance imaging, 5 Halligan S. Spence-Jones C. Kamm M.A. et al. Dynamic cystoproctography and physiological testing in women with urinary stress incontinence and urogenital prolapse. Clin Radiol. 1996; 51: 785-790 Abstract Full Text PDF PubMed Google Scholar , 6 Ganeshan A. Anderson E.M. Upponi S. et al. Imaging of obstructed defecation. Clin Radiol. 2008; 63: 18-26 Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar anorectal and colonic manometry, 2 Rao S.S. Ozturk R. Laine L. Clinical utility of diagnostic tests for constipation in adults: a systematic review. Am J Gastroenterol. 2005; 100: 1605-1615 Crossref PubMed Scopus (209) Google Scholar , 7 Rao S.S. Sadeghi P. Beaty J. et al. Ambulatory 24-h colonic manometry in slow-transit constipation. Am J Gastroenterol. 2004; 99: 2405-2416 Crossref PubMed Scopus (150) Google Scholar and colonic transit time radiological studies. Colonic segmental transit time is commonly estimated from the distribution of radio-opaque markers using abdominal radiography. This method is useful as an objective criterion for diagnosing constipation and may help to differentiate between three types of delayed transit, i.e. colonic inertia (right colon), 8 Preston D.M. Lennard-Jones J.E. Severe chronic constipation of young women: idiopathic slow transit constipation. Gut. 1986; 27: 41-48 Crossref PubMed Scopus (337) Google Scholar hindgut dysfunction (left colon), 9 Likongo Y. Devroede G. Schang J.C. et al. Hindgut dysgenesis as a cause of constipation with delayed colonic transit. Dig Dis Sci. 1986; 31: 993-1003 Crossref PubMed Scopus (13) Google Scholar and outlet obstruction (sigmoid colon and rectum). 10 Martelli H. Devroede G. Arhan P. et al. Mechanisms of idiopathic constipation: outlet obstruction. Gastroenterology. 1978; 75: 623-631 PubMed Google Scholar However, patterns of colonic hypo-motility may overlap because slow colonic transit can be secondary to impaired rectal emptying. 11 Kuijpers H.C. Bleijenberg G. de Morree H. The spastic pelvic floor syndrome. Large bowel outlet obstruction caused by pelvic floor dysfunction: a radiological study. Int J Colorectal Dis. 1986; 1: 44-48 Crossref PubMed Scopus (65) Google Scholar Colonic transit is also known to vary considerably due, for example, to dietary fibre intake, hydration, and medications, which can have a physical impact upon bowel content and flora, as well as cholinergic effects. Although the relevance of segmental transit disorders is a controversial issue, 2 Rao S.S. Ozturk R. Laine L. Clinical utility of diagnostic tests for constipation in adults: a systematic review. Am J Gastroenterol. 2005; 100: 1605-1615 Crossref PubMed Scopus (209) Google Scholar the generally accepted rationale for assessing segmental transit time is that each type of constipation calls for different types of treatment: customized medical treatment, especially for colonic inertia; biofeedback therapy, especially in pelvic floor dyssynergia-related outlet obstruction; or surgical approaches in selected cases of colonic inertia and pelvic prolapse-related outlet obstruction. Several different radiological approaches have been used to measure colonic transit times: single marker ingestion and daily radiographs, 12 Arhan P. Devroede G. Jehannin B. et al. Segmental colonic transit time. Dis Colon Rectum. 1981; 24: 625-629 Crossref PubMed Scopus (392) Google Scholar triple marker ingestions and single or double radiographs, 13 Metcalf A.M. Phillips S.F. Zinsmeister A.R. et al. Simplified assessment of segmental colonic transit. Gastroenterology. 1987; 92: 40-47 Abstract PubMed Google Scholar and sextuple marker ingestions and single radiograph. 14 Bouchoucha M. Devroede G. Arhan P. et al. What is the meaning of colorectal transit time measurement?. Dis Colon Rectum. 1992; 35: 773-782 Crossref PubMed Scopus (173) Google Scholar However, these techniques incur exposure to radiation, or may underestimate colonic transit time in cases of delayed transit. The aim of the present study was to test the reliability of a technique enabling a precise segmental count of retained markers and reduction in the exposure to radiation of patients undergoing segmental colonic transit time measurements.