Background: Gastric lipase secretion is stimulated by gastrin in plasma, but its regulation by secretin is unknown. Methods: In 7 normal persons we investigated the effect of exogenous secretin on the output of gastric lipase stimulated by intravenous gastrin-17. The gastric content was measured using a nasogastric tube for aspiration. The quantitative lipase secretion was measured by an enzyme-linked immunosorbant assay (ELISA) and the lipolytic activity by a kinetic assay. Plasma concentrations of secretin and gastrin were measured by radioimmunoassay. Results: Gastric lipase secretion (the quantity as well as the lipolytic activity) was significantly stimulated by gastrin. In response to secretin infusion, the lipolytic activity increased as acid secretion decreased. Conclusion: Secretin in postprandial concentrations does not influence the quantitative gastric lipase secretion stimulated by gastrin, but it increases lipolytic activity due to inhibition of acid secretion.