A prospective double-blind cross-over trial of oral cisapride 10 mg and placebo was performed to determine the effects of cisapride on the transit of colonic contents in normal humans. Six male volunteers were studied twice using colonic transit scintigraphy. After passing a tube to the caecum, 50 mu Ci of 111Indium diethylene triamine pentaacetic acid were instilled into the bowel lumen. The movement of radiolabelled material was followed using a gamma camera interfaced to a digital computer. Cisapride decreased the half-emptying of the caecum and ascending colon from 1.68 +/- 0.4 hours to 0.72 +/- 0.15 hours (P less than 0.05). The total colon half-emptying time was reduced from 38.5 +/- 7.2 hours to 11.1 +/- 2.9 hours on cisapride (P less than 0.05). Cisapride accelerated transit through the transverse colon, but not the descending colon. The progression of the geometric centre was faster during cisapride administration than with placebo (P less than 0.05). The number of bowel movements 48-hours-1 increased after cisapride from 2.5 +/- 0.8 to 5.0 +/- 0.4 (P less than 0.05). This study demonstrates that cisapride has a marked prokinetic effect on colonic transit in normal subjects. Cisapride may be a useful agent in the treatment of constipation.