The effects of two weeks of reduced activity on gastrointestinal transit time were studied in nine healthy elderly subjects, who had engaged in regular recreational exercise for ten years. Physical inactivity was achieved by a restriction of all kinds of physical exercise and by staying at home. Mouth-to-cecum transit time was measured by a breath hydrogen method and mean total and segmental colonic transit times by a radiopaque marker method. The mouth-to-cecum transit time did not change during the period of physical inactivity. The mean total colonic transit time (10.9 +/- 2.7 h) was significantly prolonged to 19.5 +/- 2.9 hours during the physical inactivity (p < 0.01). This prolongation was due to slowed transit through the right and the left segments of the colon. The transit time of the rectosigmoid segment of the colon was not affected. In conclusion, the period of physical inactivity prolonged the colonic transit time in active elderly subjects.