Intestinal propulsive motility was measured in rats infected with 4000 Nippostrongylus brasiliensis larvae by following the transit of radioactive chromium (51Cr) through the gut. On days 6, 8, 10, 12 and 14 post-infection, 51Cr was injected through an indwelling catheter into the duodenum. The animals were killed 15 min later and the distribution of radioactivity in the small intestine measured. A group of uninfected, catheterized animals served as controls. Intestinal propulsive activity was increased significantly on day 8 post-infection. No significant difference in the overall intestinal transit occurred on days 6, 10, 12 and 14 post-infection, although it appeared that it may have been decreased in the upper small intestine on day 6. The significance of these results is discussed.