We are conducting a clinical trial to examine the effects of hemodiafiltration on sleep apnea in dialysis patients. Fifteen patients with sleep apnea, already on dialysis will be treated with hemodiafiltration 3 times a week, instead of their regular hemodialysis treatment for a period of 3 months. We will repeat sleep studies in these patients before and after the hemodiafiltration period and assess their quality of life.