In 71 patients a partial gastrectomy was graded according to the preoperativc values of total HCl in mEq/h for maximal acid output (MAO) following large doses of histamine. In 31 males and 6 females with an MAO of 30 mEq/h or more subjected to a two-thirds gastrectomy, the average duration of dyspepsia was 13 years preoperatively. (Bleeding had occurred 1.2 times and severe vomiting 0.06 times per patient. A dietary treatment had been tried 1.6 times per patient.) Twelve months postoperatively the body weight was not significantly reduced from 71 to 67 kg. A significant increase was found for the average values of alkaline phosphatase, the thymol turbidity, and the icterus index in serum. The fecal fat showed an increase 3 months postoperatively from 7.4 to 11 g/24 h. No significant alterations were observed for the values of blood pressure, Hb, red and white blood cell counts, the sedimentation rate, serum total protein, iron, or total cholesterol. In 19 males and 15 females with MAO below 30 mEq/h subjected to one-third gastrectomy, the duration of dyspepsia was 16 years. The body weights preoperatively and 12 months postoperatively were 66 and 61.3 kg respectively. No significant increase was observed for the values of alkaline phosphatase, thymol turbidity, icterus index, or fecal fat, and the other clinical and laboratory data were not different from those found in the high secretory group. Postoperatively 97 per cent of the patients were satisfied with the result, although moderate dumping symptoms occurred in 15-20 per cent, and intolerance to milk in about 20 per cent after both types of operative procedures. The twelve-month clinical follow-up seems to show that treatment of duodenal ulcer patients with partial gastrectomy graded by the values of the augmented histamine test is a better procedure than the conventional two-thirds gastrectomy.