Intragastric instillation of coffee, decaffeinated coffee and pure caffeine in humans significantly stimulated gastric secretion. After intragastric caffeine, basal serum gastrin concentrations were not changed. However after instillation of coffee and decaffeinated coffee serum gastrin increased significantly. Thus acid secretion was significantly greater after coffee and decaffeinated coffee than after caffeine. Roasted products seem to be responsible for the gastrin-releasing effect of coffee.