Background: Previous studies present contradictory data concerning obstructive sleep apnea syndrome (OSAS), lipid oxidation and nitric oxide (NO) bioavailability. This study was aimed: (1) to compare the concentration of 8-isoprostane and total nitrate and nitrite (NOx) in plasma of middle aged males with OSAS and no other known comorbidity and carefully matched healthy controls of the same age and gender; and (2) to test the hypothesis that nasal continuous positive airway pressure (CPAP) therapy, might attenuate oxidative stress and nitrate deficiency.