The purpose of these studies was to determine the amount of saliva secreted in response to food in humans and to evaluate the effect of saliva on postprandial gastric acid secretion. Subjects chewed and spat out an appetizing steak and french-fried potato meal (modified sham feeding), with the increase in the weight of the meal during sham feeding taken to represent salivary secretion. Mean salivary flow rose from basal rates of 37.1 ml/h to 167.3 ml/h during modified sham feeding (P less than 0.001). Chewing gum increased salivary secretion to approximately the same extent as modified sham feeding, whereas chewing on plastic tubing caused a much smaller increase in salivary flow. Intravenous infusion of bethanechol (50 micrograms . kg-1 . h-1) was approximately half as potent as modified sham feeding or gum chewing in stimulating salivary flow. The salivary response to sham feeding was completely blocked by 15 micrograms/kg intravenous atropine. Salivary secretion increased approximately 20 ml/h when a 700-ml amino acid meal was infused directly into the stomach (P less than 0.01), whereas gastric distension with 700 ml saline had no effect. These findings suggested that food in the stomach or upper small intestine may activate a reflex or release a hormone into the circulation that augments salivary flow. Although intravenous gastrin-17 infusion had no effect on salivary flow, somatostatin-14 infusion increased salivary flow 15 ml/h (P less than 0.02). Saliva contained approximately 2,000 pg/ml immunoreactive urogastrone, an inhibitor of acid secretion when administered parenterally.(ABSTRACT TRUNCATED AT 250 WORDS)