The nasal valve is defined as the region of the nasal airway bounded by the caudal end of the upper lateral cartilages and the nasal septum. During inspiration this region of the nasal airway may collapse and produce a marked increase in nasal airway resistance. To define the function of this region, measurements of the nasal airway resistance in 38 subjects were performed. Using anterior mask rhinomanometry, right and left total nasal resistance, right and left upstream nasal resistance, right and left downstream nasal resistance, and right and left transmural collapsing pressure of the nasal valve were measured. Subjects who complained of nasal obstruction and had anatomical evidence of anterior nasal deformity showed a reduced level of transmural closing pressure compared with subjects complaining of no airway obstruction or those with anatomical evidence of posterior nasal deformity. This suggests that premature collapse of the nasal valve due to inadequate cartilaginous support is an important factor in producing nasal airway obstruction in individuals with anterior nasal septal abnormality. In those individuals with nasal airway obstruction and anatomical evidence of posterior nasal deformity, downstream nasal resistance was elevated compared with the asymptomatic group and the group with anatomical evidence of anterior nasal septal deformity. This paper demonstrates that premature collapse of the nasal valve is responsible for the symptom of nasal obstruction in many patients with anterior nasal septal deformity.