1. The tetradecapeptide bombesin was tested for its activity on the stomach in rats, dogs and men. On the rat stomach bombesin displayed a striking spasmogenic activity apparently independent from the autonomic nervous system. 2. In the dog the peptide was spasmogenic on the denervated Heidenhain pouch and the antrum. The inhibitory activity predominated on the innervated stomach and body fundus. 3. In man the peptide exerted a contracting effect on the antrum and the pylorus and an inhibitory effect on the stomach body and the fundus. In vitro studies performed on human stomach isolated strips showed a constant stimulant effect. 4. Apparently bombesin has a direct effect on the in situ rat stomach and on the isolated preparations, whereas it has an indirect effect on the other in situ innervated preparations.