The effects of seven different foods and three concentrations of citric acid in 16 adult subjects of each sex were evaluated. The foods were steamed rice, french fries, cheeseburger, cookie, milk chocolate, apple, and rhubarb pie. The volume of saliva was determined by subtracting the initial weight of food from that of the food bolus after subjects had chewed it normally and then spat it into a weighed container, without swallowing. The flow rates were compared with those produced in response to infusion into the mouth of 52, 156 and 260 mmol/l citric acid through a plastic tube at a constant rate of 5.0 ml/min, controlled by a peristaltic pump. Mean salivary flow rates were highest with rhubarb pie and lowest with rice; these were 70.5 +/- 11.3 and 43.2 +/- 14.4 per cent, respectively, of the maximum flow rate (7.07 +/- 2.16 ml/min) elicited by 260 mmol/l (5 per cent) citric acid. The chewing times per 10 g of food were inversely related to the water content (r = -0.82). The water content of the food bolus varied over a wide range (28-87 per cent). Thus normal foods elicit a salivary flow rate which is a high fraction of the maximum secretory rate achieved in response to acid.