Nasal inspiratory resistance and maximal inspiratory nasal flow were measured in 10 normal subjects while they breathed air and while they breathed a mixture of 80% helium and 20% O2. After the less dense helium-O2 mixture, there was a nonsignificant increase in K1 (15 +/- 93%), a 56 +/- 20% decrease in K2 (P less than 0.001), and a 48 +/- 20% increase in maximal inspiratory nasal flow (P less than 0.001). This is consistent with the accepted concept that K1 represents resistance to laminar flow and K2, resistance to nonlaminar flow (turbulent flow and/or flow due to convective acceleration), and that nonlaminar air flow predominates in the nose.