BACKGROUND AND AIMS: A number of prokinetic medications have been used to treat patients with constipation. Cisapride (C), a newer prokinetic agent, is known to enhance colonic transit, but there are a number of clinical studies on its effect on colonic rransit which are contradictionary. Misoprostol (M) is used to treat patients with peptic ulcer disea.;e but it causes diarrhea. Howevers, very little is known about the exact mechanism of cisapride or prostaglandins accelerating the colonic transit of luminal contents in humans. This study was to evaluate the effects of cisapride vs misoprostol on the movements of fecal stream. METHODS: We prospectivelir studied 10 healthy volunteers (no history of gastrointestinal disease, bowel habit. >3/week, male/female=7/3, mean age 26years). Each subject was studied twice once on cisapride (10mg tid for 2 days) and once on misoprostol (200pg qid for 2days). Each served as his or her own control. These study sessions were seperated by at least 2 weeks. Scintigraphic observativns within the first 24hours after ingestion of a pH-sensitive,methacrylate coated, delay release capsule, containing 0.25 mCi of ""'Indium labeled Amberlite pellets in unprepared colon were clone to measure the orocecal transit time (time interval between Indium capsule ingestion and dispersion of capsule in the ileocecal region) and the regional colonic transit which was defir.ed in the ascending, transverse, descending, and rectosigmoid colon. Overall total colonic transit and geometric center analysis were also done. The effect of cisapride and misoprostol upon segtnental colonic transit were then observed, and compared to controls. RESULTS: Orocecal transit time was accelerated in C group (control vs C=285+/-63 vs 157+/-14 min, p<0.01), but was not changed in M group (control vs M=285+/-63 vs 204 +45min). Total colonic transit was accelerated in M group (control vs M=1760+/-455 vs 800+/-528min, p<0.01), but was not changed in C group (control vs C=1760+/- 455 vs 1345+/-84 min). Transit from ascending colon and the progression of the geometric center were more faster after M but were unchanged after C. When compared to controls and C group, M speeds up the early filling of the transverse colon and the early emptying from the transeverse colon to the descending colon. CONCLUSIONS: Cisapride has a prokinetic effect mainly on orocecal transit, but misoprostol mainly on colonic transit.