Calcium salts were infused against a background of stimulation by histamine or porcine gastrin or against the release of endogenous gastrin (feeding test). Raising the plasma calcium to values noted in clinical chronic hyperparathyroidism did not influence histamine-stimulated secretion but had a strong inhibitory action on gastrin-stimulated secretion. In the feeding tests (endogenous gastrin) the onset of secretion was delayed by calcium infusion. The results of these experiments cannot be related directly to the problem of hyperparathyroidism, hypercalcemia, and peptic ulcer. The results do, however, indicate a difference in the stimulant actions of gastrin and histamine.