From patients who were referred to sleep lab for suspect sleep apnea, we selected 50 male patients with age> 18 y/o. with severe OSAS, which were confirmed with by overnight PSG. All were free from neurologic events, chronic pulmonary disease, active infection and substance abuse. Female patients and patients under 18 y/o were excluded. All 50 subjects were treated with 4-week CPAP. All study subjects were admitted, on the day of baseline measurement and four weeks after CPAP use, for clinical evaluation, blood sampling and PSG. And all anti-hypertensive therapy was remained unchanged during the 4-week follow-up period. Changes of parameters, before and after CPAP treatment, were compared between two groups.