The intra- and interindividual variation in the gastrointestinal transit times was measured in 12 healthy adult test subjects using a scintigraphic method with 111In marked single unit tablets. Test conditions were semi-standardized. The variation within the same individual was as large as the variation between different subjects regarding the transit times through both the small and the large intestines. The small intestine transit time was 5 h (median) with an interquartile range of 4-7 h. The median transit time through the large intestine was 23.5 h (interquartile range 19.0-40.5 h). The coefficient of repeatability for the small intestinal and large intestinal transit time was 4 h and 33 h respectively. Our conclusion is that the 111In single unit capsule method can be used for measuring the fractional gastrointestinal transit times, but the intra- and interindividual variations are rather large and similar. From a radiation-hygienic point of view the 111In single unit capsule method is acceptable. The large inter- and intraindividual variation in gastrointestinal transit time might be an important factor in the absorption of certain drugs.