Summary The concept of increased vagal activity in patients with duodenal ulceration was investigated by observing the effect of medical and surgical vagotomy on the secretion of gastrin. Using a radioimmunoassay technique fasting serum levels of gastrin were determined in 41 normal subjects, 40 patients with duodenal ulceration and 16 patients following vagotomy. The effect of atropine on gastrin secretion was observed in a further 2 patients with duodenal ulceration. The patients with duodenal ulceration were found to have elevated serum levels of gastrin. The 8 patients with “complete” vagotomy had significantly lower serum levels of gastrin than the patients with duodenal ulceration, the patients with an “incomplete” vagotomy or the normal subjects. Post‐vagotomy hypergastrinaemia was associated with a recurrence of ulceration. The abolition, by medical or surgical vagotomy, of the hypergastrinaemia associated with duodenal ulceration is consistent with the hypothesis of an increased vagal tone in this disease. These studies also suggest that gastrin estimations may be useful in predicting the presence of inadequate vagotomies.

A sensitive, specific and reproducible radioimmunoassay for secretin is described. Antibodies were readily produced against low microgram quantities of synthetic secretin. The secretin antibodies did not cross-react with the structurally similar G.I.P., V.I.P., or glucagon. Synthetic secretin was iodinated using Chloramine "T" and purified by a two-state procedure incorporating gel filtration and radient elution from a cation exchange column. Plasma samples were found to produce variable interference in the assay necessitating the incorporation of secretin-free "blands" for each patient's plasma. Production of secretin-free plasma was by incubation of plasma samples at 37 degrees C for 96 hours. The sensitivity of the assay was 12.5-25 pg/ml. Normal fasting secretin levels were 21 +/- S.E. 7 pg/ml. A mean rise in plasma secretin to 220 pg/ml was observed after intraduodenal acidification.

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