Abstract: A device for monitoring the concentration of a chemical component within a patient's physiological fluid is provided, comprising: (a) an electrode assembly for immersion within a patient's saliva, including: a ion selective electrode and a reference electrode for providing a voltage signal; and an interface element for electrically connecting the electrode assembly to a microprocessor; (b) a cup for accommodating a volume of a patient's saliva; (c) a stand element for holding the electrode assembly at a predetermined position with relation to the cup; and (d) a microprocessor for processing the voltage signal, the microprocessor determining the concentration of the chemical component within the volume of saliva and calculates the concentration of the chemical component within the physiological fluid according to a selected mathematical model.