Serum gastrin was measured by radioimmunoassay I patients after parietal cell vagotomy for active duodenal ulcer, with and without a drainage procedure, in both the basal state and following a standard protein meal. Results were compared to those of unoperated patients who had the same standard meal combined withcontinuous intragastric neutralization. In the patients with parietal cell vagotomy alone, serum gastrin rose from a basal level of 47 ± 3.4 pg/ml to a peak of 165 ± 9.1 pg/ml after the meal. In the parietal cell vagotomy with pyloroplasty group, serum gastrin rose from 42 ± 1.2 pg/ml to a peak of 173 ± 10.9 pg/ml. In the unoperated patients undergoing concomitant intragastric neutralization, serum gastrin rose from 10 ± 0.8 pg/ml to a ‘new’ basal level of 47 ± 2.5 pg/ml and then to a peak level of 166 ± 5.1 pg/ml after protein. Neither the basal levels nor those after protein were significantly different in the three groups studied. This study indicates that, after parietal cell vagotomy, there is no difference in gastrin release if the antrum is drained or undrained.