150 patients with chronic kidney disease (CKD III-IV) and 75 healthy subject is examined with both central and peripheral 24 hours blood pressure monitoring, 1 night home polygraphy to determine whether the subject has obstructive sleep apnea, and if so the degree (AHI), blood- and urine samples to determine levels of u-AQP2 og u-ENaCɣ, PRC, p-AngII, p-Aldosterone, p-Avp og p-Endothelin.