AT ANY given instant, most individuals have a unilateral nasal obstruction. This obstruction is a normal physiological phenomenon due to turbinate engorgement. The obstruction changes in a cyclical manner from side to side throughout the day and night and yet the individual is usually unaware of this occurrence. So complete is the unilateral occlusion, that effective nasal airflow at any given time is almost entirely a function of the opposite and patent nasal cavity. In this report, the effects of various pharmacological agents on the cyclical changes in nasal airway resistance are investigated. Some aspects of the regulatory mechanism of the observed cyclical changes are considered. History The earliest studies with the cyclical changes in nasal airway patency were performed by R. Kayser1 in 1895. He estimated nasal airway resistances by comparing the time required to draw known equivalent quantities of air through each nostril with small calibrated bellows.