125 patients (78 men and 47 women) aged 18 - 65 years, with diagnosed resistant hypertension and moderate or severe OSA were included in the study, which was conducted in years 2014-2017 in the Department of Hypertension, Angiology and Internal Medicine and the Department of Pulmonology, Allergology and Respiratory Oncology at the University of Medical Sciences in Poznan, Poland. 23 patients did not complete the study because they did not meet the inclusion criteria (10 patients) and did not follow the recommendations (13 patients). 102 patients were randomized to two groups. In Group A, 50mg Eplerenone was administered orally once a day additionally for standard antihypertensive therapy. In Group B, standard antihypertensive therapy was not changed for 6 months of follow-up. RAH was recognized when in spite of the use of at least 3 antihypertensive agents (including a diuretic) in maximum doses, it was impossible to achieve the target values of BP (< 140/90 mmHg). The patients were taking on average 3,93 antihypertensive medications including diuretics (100% of patients), angiotensin-converting enzyme inhibitors (54% of patients), angiotensin II receptor antagonists (45.2% of patients), calcium antagonists (83.9% of patients), β-blockers (77.4% of patients), and α-blockers (22.6% of patients). The permission no. 565/14 to conduct the study was granted by the Ethics Committee of the University of Medical Sciences in Poznan. All patients gave an informed and written consent to participation in the study. Blood pressure measurements In all patients, during each visit, BP measurements were performed three times at rest in supine position, in standard conditions, using an upper arm blood pressure monitor BP monitor (Omron 705IT, Omron Healthcare, Kyoto, Japan). Ambulatory 24-hours BP automated monitoring (ABPM) was performed using a 24-hour ambulatory peripheral BP monitor TM2430 (A&D Medical, San Jose, California, United States). The frequency of measurements was every 15 minutes between 7:00 and 22:00 and every 30 minutes between 22:00 and 7:00.