Sleep-disordered breathing (SDB) is associated with nitric oxide-mediated endothelial dysfunction and increased risk and prevalence of cardiovascular disease, namely, arterial hypertension. A substantial number of patients do not comply with nasal continuous positive airway pressure (nCPAP) treatment. These individuals have a persisting increased cardiovascular risk. Antihypertensive drugs have shown to improve nitric oxide-mediated endothelial dysfunction. We therefore designed a study to test the hypothesis that antihypertensive drug treatment in hypertensive patients with SDB can have beneficial effects on nitric oxide-mediated endothelial function in the absence of treatment with nCPAP. Six patients with SDB and treated arterial hypertension, six normotensive patients with SDB, and six healthy controls received sleep studies and an assessment of venodilation using the dorsal hand vein technique. Polygraphic measures using standard overnight sleep studies and dose-response curves to the endothelium-dependent vasodilator bradykinin were obtained. Maximum nitric-oxide-mediated dilation to bradykinin was significantly higher in patients with SDB who had received antihypertensive drug treatment compared to normotensive SDB patients. Nitric oxide-mediated dilation in hypertensive patients with SDB was similar to nitric oxide-mediated dilation in healthy controls. After treatment of normotensive patients with SDB using nCPAP, nitric oxide-mediated dilation in normotensive SDB patients was comparable to nitric oxide-mediated dilation in SDB patients with antihypertensive drug treatment and normal controls. Hypertensive patients with SDB present a normal nitric oxide-mediated endothelial function under antihypertensive treatment.