The present study deals with the behaviour of the erectile tissue of the nasal mucosa in the normal rat and after selective transection of the autonomic nerve supply, measured with physiological and histometrical techniques. In the normal animal cyclic changes in the patency of the nasal lumen occurs with a cyclus time of 61 min, disturbances being observed in this rhythm a few weeks after transection of the various autonomic nerves. Selective transection of the main route of the sympathetic or the parasympathetic systems results in a dominance of the antagonist (congestion or decongestion). Transection of both systems does not result in a significant change in the dilated state of the nasal cavity from normal, although the cyclic activity disappears. A tendency towards a normal nasal cycle was observed several months after transection.