In conscious rats with innervated total gastric pouches, intravenous infusion or duodenal intubation with fat and glucose decreased gastric acid secretion while amino acids produced the opposite effect. Intravenous infusion of amino acids strongly increased plasma gastrin, but fat and glucose had no effect. Plasma gastrin increased after duodenal intubation with all three nutrients, amino acids being the most effective. Mechanisms of action of gastrin release and acid secretion are discussed concerning the route of nutrients administration which could play a role in the liberation of known or unknown stimulatory or inhibitory factors from intestinal cells.