Some years ago, a test procedure was developed in this laboratory, for differentiating from completely vagotomized gastric pouches in dogs. This test was based on the secretory response following the induction of a suitable degree of insulin-induced hypoglycemia!. Subsequently, the procedure was adapted for use in patients with peptic ulcer2 to determine whether vagotomy was physiologically complete following apparently total anatomical interruption of the vagus nerves. It is generally accepted that the response depends on the stimulation of a gastric secretory center in the brain by the hypoglycemia, and the transmission of the resulting impulses via the vagi to the gastric mucosa. Considerable experimental evidence exists to indicate that complete division of the vagi in the dog eliminates this response, and that incomplete division fails to do so. For example, pouches constructed so as to preserve innervation gave a positive response to insulin hypoglycemia, whereas those in which all intramural vagus fibers had been severed, failed to do so. It was also shown that such vagal pouches gave positive responses whether they retained almost the entire vagus supply, as in the type of pouch designed by us3, or only a small fraction of that innervation, as in the Pavlov pouch. In man, the evidence that complete division of the trunks eliminates the response to hypoglycemia is not so conclusive as in dogs, in which the experimental methods are more precise. The latter is confused by the anatomical variations in vagus distribution about the lower esophagus, and possibly also by the existence of cholinergic fibers to the stomach which accompany its sympathetic innervation, the presence of which may be expected to give a positive insulin test despite complete vagotomy at the diaphragmatic level. The purpose of the present investigation was to determine the frequency with which complete interruption of parasympathetic function in man, as measured by acid-secretory activity in the insulin test, resulted after vagotomy, and to correlate clinical findings and the results of the test. * Read at the Annual Meeting of the American Gastroenterological Association, June 3, 1949, Atlantic City, New Jersey. t This investigation was supported in part by a grant from The Altman Foundation of New York.