In dogs with pH-electrodes indwelled in different portions of the stomach and duodenum, the zone of maximal hydrochloric acid formation was found in the angle area of the minor curvature. The bottom area of the stomach also revealed a high acid-forming function. The intrastomach milieu on the major curvature from the body till antral portion revealed a significantly lesser acidity. The pyloric glands of the antral portion produce a weakly alkaline secret neutralizing the secret of acid-forming zone. The borders of the neutralizing zone on the stomach minor curvature are variable.