The lateral wall of the nostril is considered as the functional unit in the regulation of the nasal resistance causing more than half of the total resistance. In 16 test-subjects both nostrils were dilated with a plastic nasal device, Nozovent, and the airflow through the nose was measured with and without the device. In each object the mean value of ten inspirations at 150 Pa was calculated. Before the application the mean value of the subjects was 0.68 l/sec and with the device 0.84 l/sec. The improvement of airflow was comparable with that of treatment with nose-drops. The device ought to be helpful in patients with or without collapsing ala nasi during the night to increase nasal airflow when sleeping.