We studied the transit of a radioactive test solution in the gastrointestinal tract under conditions expected to alter propulsion, autonomic drugs, morphine, chlorpromazine-induced enteromegaly, indomethacin-induced small intestinal ulceration, ileal obstruction, postirradiation, and fasting. The radioactive test solution was introduced into the stomach or duodenum of rats, and, after a period of time, the stomach and intestines were removed. The distribution of radioactivity was measured by passing the gastrointestinal tract under a scintillation detector and graphically recording the count rate. By comparison of results of intragastric and intraduodenal administration of test solution, variations in gastric emptying were shown to limit the value of studying small intestinal propulsion by intragastric administration of test solution. Mecamylamine, chlorisondamine, and morphine produced significant retardation in propulsion by both techniques. Tolazoline and neostigmine produced acceleration of net propulsion by the intragastric technique, but not by the intraduodenal method. Even though the intestine was dilated after 6 weeks of chlorpromazine treatment, gastrointestinal propulsion was not altered. When ulcers produced by indomethacin did not obstruct the lumen, the test solution passed through the bowel faster than in controls. When the test solution was placed in the stomach of irradiated rats, there was marked gastric retention, but small intestinal transit was markedly accelerated when the solution was put into the duodenum. The intraduodenal technique is not technically difficult and appears to be an improved method for quantification of small intestinal propulsive motility.