A method and apparatus for producing a stream of heated vapor involve the steps of operating an ultrasonic generator (74) while submerged in a pool of the liquid to be vaporized in a chamber (14) to produce a spout (76) of intensely-agitated liquid spouting upwardly out of the surface (22) of the liquid in the chamber (14); directing a confined stream of hot gas into the chamber (14) to impinge the liquid spout (76) and to thereby vaporize liquid therein; and outletting from the chamber (14) a confined stream of hot gas saturated with the vapor and mixed with a small quantity of liquid droplets. The described method and apparatus are particularly useful for treating the common cold by applying the so produced stream via a delivery tube (80), with the stream so shaped and pressurized that the stream is propelled to the nasal mucosa.