This study examined the effect of a high dietary intake of calcium (1.5-2% of diet) or of an i.p. injection of calcium lactate (65 mg Ca/kg) on gastric acid secretion in the conscious, unoperated rat. Two weeks on the high-calcium diet inhibited basal acid secretion in comparison with calcium-free or low-calcium diets. This inhibition was reversed upon feeding a lower level of calcium to the rats. A high-calcium injection into rats fed a commercial diet inhibited histamine-stimulated acid secretion, but not basal secretion. The combined effects of high dietary calcium and a high-calcium injection was also studied. On a calcium-free diet, the calcium injection inhibited both basal and histamine-induced acid secretion. On a 2% calcium diet the high-calcium injection inhibited only the histamine-induced, but not the basal acid secretion. © 1990 Pergamon Press plc.