By means of the acoustic reflection technique, termed acoustic rhinometry, cross-sectional areas along the whole upper airway can be measured by an acoustic click. This paper describes the normal values obtained from 134 probands. The normal curve shows the minimal cross-sectional area (I-notch) to be located at the isthmus nasi. The second narrowest segment of the nasal cavity is located at the head of the inferior concha (C-notch). In patients with turbinate hypertrophy due to allergic or vasomotor rhinitis the minimal cross-sectional area is sited at the head of the inferior turbinate. Furthermore, acoustic rhinometry allows exact measurements of size and location of the congested mucosa following challenge with allergens in patients affected with allergic rhinitis. After anterior turbinoplasty of patients with turbinate hypertrophy improved nasal breathing was associated with an enlargement of the cross-sectional areas at the head of the anterior inferior turbinate. Acoustic rhinometry not only enables to distinguish the various deviations of the nasal structures from normal (valve stenosis, septal deviation, turbinate hypertrophy, tumour masses) concerning their location and size, but also allows to demonstrate exactly the efficacy of rhinosurgical techniques.