The resistance to air flow of each nasal passage in the anaesthetized pig was determined by pumping air through the nose and measuring pressure changes in nasal cannulae. A nasal cycle was observed in the marjority of the pigs. Three types of change in nasal resistance were observed and their possible causes are discussed. Section of the right cervical sympathetic nerve abolished the cyclic changes in nasal resistance of both nasal passages. The method described may prove useful in studying the physiology of the nasal cycle.