The nose in man, despite its unusual external appearance, has a variety of functions that are related to its unique internal anatomy and the vascular tone of its mucous membrane. In addition, it houses the receptor side of the first cranial nerve. This receptor is relatively primitive in man and probably less effective in monitoring his environment than that of other mammals. The nose is the portal by which the ambient air first enters the body. The nose functions as a "guard dog" or "watch dog" for the lungs. It conditions air to a specific range of temperature and humidity. Its protective filtration and ciliary mechanisms are abundant. Nasal reflex functions affect the lower respiratory tract and cardiopulmonary functions and respond to intense emotional situations. Since the time of Proetz' original essays on the physiology of the nose, a great deal of study has been done on the various and myriad functions of the nose. A working understanding of its peculiar anatomy and unusual functions are important for understanding the pathophysiology of nasal disease.