The National Institutes of Health (NIH) sponsored HEMO Study did not demonstrate that an increase in dialysis dose was associated with an improvement in patient mortality rates. Despite this negative result, there is ongoing interest in determining if still higher doses of dialysis may be of benefit to patients receiving chronic hemodialysis therapy. Testing this hypothesis requires the use of more fre-quent hemodialysis and/or a much longer duration for each dialysis session. "Short daily hemodialysis", actually six times per week hemodialysis for 1.5 to 3 hours per session, provides a significant increase in small molecule clearance as measured by urea kinetics. "Long nocturnal daily hemodialysis", actually six times per week hemodialysis for 6-8 hours per session, provides a significant increase in both small and large molecular weight clearance and often alleviates the need to take phosphate binders. Both forms of more frequent dialysis have been shown to improve control of blood pressure. One small randomized trial of nocturnal versus conventional home dialysis showed a decrease in left ventricular (LV) mass at 6 months in the nocturnal arm only. Most clinical trials conducted in these dialysis modalities have been observational trials and have enrolled small numbers of patients. The National Institutes of Health is sponsoring two clinical trials via the Frequent Hemodialysis Network to determine the effect of these two more frequent dialysis modalities on intermediate outcomes. In the short daily study, 250 patients will be randomized to receive either six times per week HD, with a session length of 1.5 to 2.75 hours, or conventional in-center hemodialysis. In the nocturnal study, 150 patients will be randomized to receive either six times per week overnight dialysis, with a session length of at least 6 hours, or conventional home hemodialysis.