In a double-blind trial, 12 out-patients with primary anorexia nervosa received, for six weeks, either 10 mg cisapride or placebo, three times a day. Cisapride accelerated gastric emptying of a radiolabelled semisolid meal in all six patients; five gained weight and symptoms of gastric retention ameliorated in four. With placebo, three of six had emptying enhanced, four gained weight, and one's symptoms improved. For another six weeks, all patients received cisapride. In five of the patients who had received cisapride, emptying further accelerated or remained stable; in one it slowed. Of the six patients who received placebo, four had emptying accelerated, five gained weight, and symptoms improved in four. Longer administration of cisapride may, by enhancing gastric motor activity, alleviate symptoms of retention and thus help to change eating behaviour.