Assessment of total and segmental colonic transit times (CTT) in man using a single type of radiopaque marker and one abdominal X-ray has been validated but not extensively studied. The aims of our prospective study were to establish normal values of this method as a function of age, gender and fiber intake in healthy subjects. Eighty-two healthy volunteers (51 men, 31 women, mean age 38 yr, range 21-61) with normal stool frequency (between 3/day and 3/week) and no history of gastrointestinal disease or medication were enrolled and ingested 10 small (3 mm edge) radiopaque markers every morning for 6 consecutive days. On the 7th day, an abdominal X-ray was performed to calculate total and segmental (right, left, rectosigmoid) CTT according to Arhan's method (CCT = 2.4 N; N = number of markers in the considered zone). During the study the number of stools was recorded and fiber intake estimated on a questionnaire. Stool frequency, total and segmental CTT were evaluated for differences due to age, gender and/or fiber intake. In volunteers, total, left and rectosigmoid CTT were closely related to stool frequency (P = 0.0001) being longer in women than in men (P < 0.02). In contrast, right CTT was independent of gender or stool frequency. Finally, in this group CTT were independent of age and fiber intake. This study confirms the influence of gender on CTT and demonstrate the ability of this simple and non-invasive method (0.08 mrad surface exposure) to assess CTT. Its use as a diagnostic tool in self-defined constipated patients would be of interest in clinical practice.