Management of patients with multiple endocrine neoplasia type I (Wermer's syndrome) who have concurrent hypercalcemia and hypergastrinemia is controversial. The usual therapeutic approach has been to perform parathyroidectomy first before surgery for ulcer disease in an effort to decrease serum calcium concentration and presumably remove one of the stimuli for both gastrin and gastric acid secretion. We present the history of a 48-year-old man with primary hyperparathyroidism and Zollinger-Ellison syndrome who underwent acid secretory studies and secretin stimulation tests before and after parathyroidectomy. We also studied the effect of calcium channel blockade on gastrin and gastric acid secretion, since calcium influx into endocrine cells, such as the gastrinoma cell, is thought to be critical in hormone secretion. Although parathyroidectomy reduced serum calcium and parathormone levels to normal, basal serum gastrin concentration and basal acid output remained unchanged. The peak rise in serum gastrin concentration after secretin injection was less after parathyroidectomy than before parathyroidectomy but was still abnormal. During administration of verapamil, a calcium channel antagonist, no change was seen in the serum gastrin concentration, secretin test response, or acid secretion. Basal acid output was 45.4 mmol/hr before parathyroidectomy or verapamil and 54.0 and 50.4 mmol/hr after parathyroidectomy or verapamil, respectively. In contrast, a small but significant decrease (p less than 0.05) in serum parathormone concentration occurred during treatment with verapamil, an observation that to the best of our knowledge has not been previously reported in humans.