The present study shows that a single oral recommended dose of propantheline bromide normally doubles the mean gastric half-emptying time in man. In a prospective, double-blind, randomized crossover design 13 normal subjects were given 30 mg propantheline or placebo 90 min before taking a 113m-indium-labeled liquid test meal, the volume of which was adjusted to body weight. The disappearance of radioisotope from the area of the stomach was determined by external gamma counting. After placebo the mean half-emptying time was 68 min and after propantheline it was 135 min (p less than 0.005). Although salivary flow decreased and pulse rate increased there were no visual disturbances. In studies already reported maximally tolerated oral doses of quaternary ammonium anticholinergic drugs have not consistently retarded gastric emptying in man.