Abstract: A pass-over humidifier for delivering a supply of heated, humidified air through an elongated conduit to a mask worn by a patient. The humidifier is designed for wear by a patient during sleep to treat chronic breathing disorders such as allergic rhinitis. A supply of air is drawn into a humidification chamber by a fan and is passed over the surface of a water reservoir where it picks up moisture. The moisture-laden air is mixed with a stream of relatively dry heated air within the humidifier to form a humidified air stream. The humidified air stream is discharged from the humidifier into the elongate conduit at a temperature within the range of approximately 45-57° C. and at a relative humidity within the range of approximately 25-55%. Since the humidified air is preferably heated to a temperature exceeding 45° C., the humidifier is essentially self-sterilizing. The temperature of the humidified air stream drops significantly as it passes tough the conduit between the humidifier and the mask.