The effects were studied on lung volumes of partial (chronic) nasal obstruction, total overnight nasal occlusion with a nasal pack, and interdental wiring for 6-8 weeks. Total lung capacity, functional residual capacity, and residual volume decreased significantly with total nasal occlusion and with surgical relief of chronic nasal obstruction. All three volumes increased with interdental wiring. It is concluded that these effects are a result of changes in oronasal resistance: lung volume is enlarged by an overall increase in resistance and diminished by a decrease in resistance. These findings imply that the resistance to expiration provided by the nose helps maintain lung volumes and so may indirectly determine arterial oxygenation.