A method for continuous monitoring and recording of ventilation rate and tidal volume in spontaneously breathing anesthetized rats is described. The system is based on a hot wire flow meter placed in connection with the tracheotomy tube. In cardiovascular experiments routine monitoring of ventilation was found useful in the following instances: 1) detection of ventilatory disorders, 2) detection of central effects of drugs, 3) interpretation of results in cases where cardiovascular drugs alter ventilatory function.