Seven male Rhesus monkeys, with demonstrated gastric hypersecretory response to 50% distal small bowel resection, were studied. This increase in gastric acid output had persisted for more than 6 months. Precise, anatomical antrectomy without vagotomy was performed and intestinal continuity restored by gastroduodenostomy. Complete abolition of basal acid secretion and of the secretory response to histamine occurred. These effects could not be reversed by continuous (5 hour) infusions of pentagastrin at 0.2 microgram/kg hr-1 or 2 microgram/kg hr-1. The dose response curve to gastrin pentapeptide was altered; maximum secretion was greatly reduced and occurred at 10 microgram/kg hr-1. Neither basal serum gastrin or basal serum GIP was significantly reduced by antrectomy. These findings indicate that in this animal model the antrum is essential in the genesis of the hypersecretory state. If these findings are relevant to man precise antrectomy may be the procedure of choice for symptomatic acid hypersecretion after small bowel resection or disease.