Abstract: A method and an apparatus are described which are useful for respiratory tract therapy. The method comprises contact of mucous membranes with vapor-phase water in the substantial absence of nucleating water-vapor condensation particulate, and includes the use of a heated delivery tube, unheated nasal cannula, for the delivery of a nasal cannula vapor/gas stream to a nasal passageway at delivery rates in excess of 8 liters per minute at dew point temperatures equal to or less than dry bulb temperatures and heating of a delivery tube vapor-gas stream to a temperature sufficiently greater than the canula nare dew point use temperature in order to cause a readily observable cannula condensation film to form near the exit use ports thereby signaling that the appropriate cannula delivery stream dew point-dry bulb temperature differential exists which insures that the dry bulb nare exit temperature is equal to or greater than the nare dew point use temperature.