The basic and with pentagastrin stimulated (dose response) secretion of acid and proteolytic activity of the stomach were estimated at five healthy volunteers before and after a six-week-antacid-therapy as well as at ten patients with duodenal ulcer disease. After a six-week-antacid-therapy the BAO and the basic proteolytic activity were reduced for 50% as compared to the healthy volunteers without it while the maximal stimulated secretion of acid and proteolytic enzymes was not altered. After a three-day-antacid-therapy these changes did not occur. The basic acid output (BAO) was increased for 60% and the basic secretion of proteolytic enzymes was increased for 50% at duodenal ulcer patients. The changes of the gastric juice volumes at the different steps of stimulation and within the three groups of patients do not seem to be correlated constantly to the changes of secretion of acid and proteolytic activity. After a three-day-antacid-therapy, however, the volume of the basic and stimulated gastric juice turned out to be identically reduced as after a longtime antacid therapy. These results suggest that the secretion of acid, proteolytic activity and gastric juice occur independently.