Examination of rhinomanometric records of 2500 referred adult patients revealed 891 unobstructed noses (Rn <0.25 Pa/cm3/sec). Topical decongestant reduced respiratory airflow resistances of these noses by ⅓ on average indicating the extent of the vascular component. Alar retraction, which minimizes resistance of the compliant portion of the nose, reduced unilateral nasal resistances by as much as ⅔, establishing the alar lumen as a major resistive segment of the unobstructed nasal airway. The nasal resistances that persisted after decongestion and alar retraction predominated in the immediately adjacent cavum. There remained 1350 noses designated as obstructed by clinician assessment of the records and suitable for analysis. Application of topical decongestant, which minimized the mucovascular component of resistance, revealed ⅘ of residual obstructions to be principally unilateral and were designated as structural. Half these structural obstructions were restricted to the alar lumen and half included the alar lumen and the adjoining cavum. Obstructions confined to the cavum were less than 2%. A further ⅕ of the nasal obstructions were bilateral and their resistances, which were markedly elevated in many cases, were substantially reduced by topical decongestant indicating an extensive vascular component. They were designated as mucosal.