Total nasal resistance measurements in 40 patients with obstructive sleep apnea syndrome (OSA) and 31 non-snorers were performed.Active anterior rhinomanometry was performed with a Nippon Kohden MPR-2100 rhinomanometer to measure inspiratory and expiratory total nasal resistance in both the upright and the supine positions.Nasal resistance values of each nostril were measured at a fixed pressure gradient sample point of 1.0cm H2O. Total nasal resistance values were calculated by a formula.Of the 40 OSA patients 24 were treated surgically, two with tonsillectomy, one with uvuloplasty, and 21 with uvulopalatopharyngoplasty (UPPP).The mean total nasal resistance values were compared between the 40 OSA patients and the 31 non-snorers, and before and two months after operation in 24 OSA patients treated surgically.The mean expiratory and inspiratory total nasal resistance values of the 40 OSA patients were significantly higher than those of the 31 non-snorers in both the upright and the supine positions.There was no correlation between the apnea index and the nasal resistance values in the 40 OSA patients.In the 24 OSA patients treated surgically there was no significant difference in nasal resistance before and two months after the operation.