Upper respiratory infections make up 90 per cent of the practice of the general medical doctor during the winter months. The common cold and related complications lead the list of causes of acute morbidity during the cold weather. The medical expense resulting from these ailments is a substantial part of the cost of health care, which is in urgent need of containment. Man, migrating from the warm climates of his origin, quickly learned how to protect himself against the cold but is still very much remiss in compensating for the low humidity created by indoor heating. A viral etiology for the common cold has been established, but efforts to produce an effective vaccine have failed except in special circumstances. It has been shown, however, that the virus is destroyed in the presence of adequate humidification. Furthermore, maintenance of proper indoor humidity will not only improve health but will also act to make more acceptable the 65 degrees F. limit to indoor heating newly mandated by law as an energy conservation measure. A graphic representation and pertinent relative humidity tables are used to develop the subject.