Several methods have been described to measure colonic transit times. The physical properties of all types of markers used allow to analyze and quantify them in stool samples or in the colon. The selective measurement of colonic (ceco-anal) transit time requires complicated intubation techniques. For most purposes it is sufficient to approximate the colonic transit by the whole gut transit, since oro-cecal transit time usually is only about a tenth of whole gut transit time. For this purpose the marker can be administered orally. In order to measure segmental colonic transit times it is necessary to monitor the distribution of the markers within the colon. For that purpose scintigraphic techniques are suited, but they require special equipment and are time consuming. Radio-opaque pellets, in contrast, are cheap, easy to handle, and have no known side effects. The following procedure is recommended: the patient swallows a gelatin capsule which contains 20 radio-opaque pellets on each of 6 consecutive days at the same time when on day seven a single abdominal x-ray is obtained. Then, segmental and total colonic transit times can be calculated from the number of retained pellets.