Patients with peptic ulcer disease are often advised to avoid cola, coffee, and alcoholic beverages. However, the effect of many popular beverages on gastric acid secretion has not been systematically studied. This study was undertaken to determine the effect of nine commonly ingested beverages on gastric acid secretion in humans. Six healthy subjects were each studied on 11 separate days and in random order. Test substances included 360 ml of Coke, Tab, 7-Up, instant Maxwell House coffee (4.5 g), instant Kava coffee (4.5g), instant Sanka coffee (4.5 g), tea (4.25 g), milk, and beer. Water served as a control. Mean ± SE maximal acid output to pentagastric was 27.0 ± 6.1 mmollh. Each beverage was swallowed at its usually consumed temperature. Gastric acid secretion was measured by intragastric titration until either the liquid had left the stomach or for 1 h. Phenol red was used as a marker to measure emptying. All beverages had emptied by >90% by 1 h, except milk that had emptied by 77%. Gastric acid secretion during the 3.5 h after each beverage was significantly (p < 0.05) greater than the water control. Tab, coffee, Kava, beer, and milk increased gastric acid secretion to >70% of maximum acid output to pentagastrin while beer and milk increased gastric acid secretion to >95% of the pentagastrin response. Several properties of each beverage were determined: calorie and caffeine content, osmolality, ionized calcium, initial pH, and buffering capacity to pH 1.5. No single property was an adequate predictor of the secretory response. It was concluded that many commonly ingested beverages are potent stimuli of gastric acid secretion.