We introduce the standard method of measurement of nitric oxide recommended by American thoracic society in 1999 and report the results of exhaled NO and nasal NO in patients with obstructive sleep apnea syndrome(OSAS). Our data showed lower exhaled NO output in the patients with OSAS than that of normal volunteers(NV) and that of patients with simple obesity(SO). On the other hand, nasal NO in the OSAS patients is higher than that of NV and that of SO patients. Also, there were significant relationships between apnea index and exhaled NO and between desaturation during sleep and nasal NO. These findings suggested that NO from lower and upper airway will be a non-invasive maker of sleep disordered breathing in future.