1. The changes in plasma enteroglucagon concentration and plasma volume were measured after oral glucose in sixteen subjects before and forty-eight subjects after operative treatment for benign duodenal ulceration. Truncal vagotomy with a drainage procedure had been performed in sixteen of the postoperative subjects studied, selective vagotomy with a drainage procedure in seventeen, and partial gastrectomy in fifteen. 2. Patients in whom the glucose produced dumping symptoms had significantly greater enteroglucagon concentrations than those who were symptom-free, which confirms the results of a preliminary study. There was a highly significant correlation between the rate of rise of plasma enteroglucagon and the rate of fall of plasma volume. 3. There was no difference in the rate of rise or in peak plasma enteroglucagon concentration between the groups of patients who had different operative procedures. This suggests that enteroglucagon release is not under vagal influence. 4. There was no apparent relation between the plasma enteroglucagon concentration and the time-interval between the operation and the time of study, which implies that the exaggerated release of enteroglucagon after operation occurs in response to the altered gastric physiology and that there is minimal adaptive change.