Ten patients with postprandial upper abdominal discomfort, 4 of them having delayed gastric emptying, were included in a single-blind y camera study aimed at comparing the effects of cisapride and metoclopramide on gastric emptying. The two drugs were given sequentially, at a one-week interval, at a single oral dose of 10 mg, 15 minutes before intake of a labelled ordinary test meal. Applying a power exponential mathematical model to the y-camera data, T1/2 and the shape of the emptying curve were determined. The median half-emptying time (T1/2) was reduced from 81.5 min. in the basal condition to 62.5 min (-23%) after cisapride and to 84.5 min. (-9%) after metoclopramide. As compared with the basal values cisapride significantly (P less than 0005, Wilcoxon Test) reduced the % RRAD from 45 min. after intake of the meal on wards. The onset of action of cisapride was faster (P less than 0.05) than that of metoclopramide. In the main, each of these drugs accelerated evacuation of the meal in the cases of delayed emptying. Cisapride particularly shortened the initial emptying lag and was superior to metoclopramide in this respect.