The effect of humidity and temperature of inhaled air on perceived acceptability of the air was studied. Thirty-eight subjects evaluated air at 14 combinations of temperature and humidity to verify that insufficient evaporative and convective cooling of the mucous membranes in the upper respiratory tract is a cause of local warm discomfort and of a perception of poor air quality. Unpolluted, conditioned air was led from a climate chamber to a box where the subjects one by one evaluated the air. The inhaled air was rated warmer, more stuffy and less acceptable with increasing air humidity and temperature. A model was developed that predicts the percentage of persons dissatisfied due to insufficient respiratory cooling as a function of the actual evaporative and convective cooling of the respiratory tract. Together with a previously proposed model for predicting discomfort due to high skin humidity, the respiratory model may be used to specify upper limits for humidity in the indoor environment.