The effects of nasal valve dilation on snoring and obstructed breathing were studied in 11 patients with habitual snoring and/or obstructive sleep apnea. The anterior part of the nose, the valve region, was dilated by means of a plastic device. Ten patients underwent polysomnographic investigation including pulse oximetry and measurement of snoring noise with and without the nasal dilator in a randomized manner. Snoring, nocturnal arousals, and daytime hypersomnolence were rated by the patient and partner on a questionnaire before and after a 10-day treatment period with the dilator. The nasal airflow, as assessed by rhinomanometry when awake in the sitting position, increased by 18% (range, 5.5% to 45%) when the nasal dilator was used. The frequency and severity of obstructed breathing decreased significantly with the nasal dilator. The apnea index with and without the nasal dilator was 6.4 (range, 1.3 to 15) and 18 (range, 1.8 to 60), respectively. The mean decrease of the apnea index was 47%. The overnight minimum arterial oxygen saturation (with and without the nasal dilator was 84% (range, 76% to 88%) and 78% (range, 68% to 89%), respectively. There was a substantial decrease in snoring noise (number of epochs with Leq values, equal energy level, above 55 or 60 dB) with the dilator in all patients who presented with snoring noise above these levels during the control night. No subjective effects on arousal frequency or daytime hypersomnolence were reported. Four of 11 patients were positive to continue using the nasal dilator.