This paper discusses methods for collection of both whole saliva and individual gland secretions, the normal ranges of salivary flow rate, the effects of physiological variables which influence flow rate, and the role of saliva in oral sugar clearance. The physiological basis for the sensation of dry mouth is discussed, and a new concept is advanced which states that the sensation of dry mouth will occur when the salivary flow rate is less than the sum of the rates of water absorption and evaporation from the mouth. In a study of the effects of anticholinergic agents on salivary flow, the subjects experienced the sensation of dry mouth when the normal flow rate of unstimulated saliva was reduced by from 40 to 50%.