A method and system for the application of molecular sieves to the removal of carbon dioxide and carbon monoxide from the patient expired gases during anesthesia. The system is especially useful in anesthesia using any of the halogenated ether inhalation anesthetic agents. The expired gases are dried using a non-reactive desiccant to remove water, passed through a filter capable of removing particles larger than 0.3 microns, passed through a bed containing either natural or synthetic molecular sieves capable of removing carbon dioxide and carbon monoxide and then returned to the breathing circuit for recirculation to the patient.