Sleep apnea, which affects 10% of men in the mean age group, is a common illness, and arterial hypertension one of its early symptoms. For the large group of, mainly young, patients with mild to moderate sleep apnea and arterial hypertension it is important to have a drug treatment available which will effectively control blood pressure without exacerbating symptoms of sleep apnea. We studied the effects of antihypertensive agents on blood pressure, sleep and sleep apnea in a randomized double-blind study of 24 patients with a sleep apnea acitivty of more than 10 apnea phases per hour of sleep and arterial hypertension with diastolic blood pressure values in the sitting position ≧ 95 mm Hg. Mean age was 51 (range: 33–69) years, mean body mass index 31.4 (24.9–40.6) kg/m2. The study protocol envisaged two baseline measurements in the sleep laboratory, after which the medication was administered for 8 days. On the last 2 days of the treatment, polysomnographic leads were once again recorded in the sleep laboratory. The patients received either the β-blocker metoprolol (1 × 100 mg/day) or the angiotensin-converting enzyme inhibitor cilazapril (1 × 2.5 mg/day). Systolic and diastolic blood pressure were decreased by both substances as expected. Total sleep time was 358 (233–425) min vs. 332 (255–383) min in the metoprolol group and 368 (295–424) min vs. 341 (265–434) min in the cilazapril group which is statistically not different between the two groups nor between the proportions of non-REM and REM sleep. Sleep apnea activity was 40 (15–91) vs. 26 (0–57) apneas/h of sleep in the metoprolol group and 40 (12–84) vs. 27 (0–72) apneas/h in the cilazapril group, which is a significant decrease for both groups (p < 0.01). Further investigation has to explore detailed blood pressure analysis by invasive means in dependence on sleep stages and nocturnal breathing disorders under antihypertensive treatment. For the large group of patients with nocturnal breathing disorders, the knowledge of possible side effects of an antihypertensive therapy is essential.