The invention relates to a method for monitoring the functioning of sensors for the measurement and monitoring of state parameters of liquids or gases, especially in the field of process measurement technology, for example of electrochemical, electrophysical or optical sensors, wherein the sensor is placed into a test state at time intervals and test parameters are registered, or these test parameters are registered at time intervals in the course of the measured value registration, wherein the registered parameters are stored and a backwards-looking, chronological development of the stored test parameters is evaluated for performing the functional monitoring and the development of sensor behavior to be expected in the future is predicted therefrom and information concerning the duration of the remaining, disturbance-free operation of the sensor is obtained.