Acute renal failure (ARF) occurs in 5-7% of all hospitalized patients and is associated with a terrible prognosis. The nutritional status of ARF patients has been proposed to be an important determinant of subsequent morbidity and mortality. While the nutritional hallmark of critically ill patients with ARF is extreme hypercatabolism, malnutrition can also develop due to both inadequate protein and calorie supplementation, and diminished utilization of available nutrients. The long-term objectives of this proposal are to identify specific markers of catabolic stress and malnutrition that best correlate with adverse outcomes, and establish the extent to which negative nitrogen and energy balance contribute to increased morbidity and mortality in ARF patients. The specific aims are: (1) to examine the utility of specific markers of nutritional status and catabolic stress in assessing the efficacy of nutritional therapy and in predicting outcome in ARF patients; (2) to examine the interrelationship between the etiology of ARF associated with co-morbid conditions and characteristics of renal replacement therapy on the level of catabolism and nutritional parameters in ARF patients; (3) to examine the impact of nitrogen balance on outcome in ARF patients; and (4) to evaluate feasibility of implementing an optimized nutritional assessment and prescription protocol in ARF patients. The research design of this proposal includes a 3 month lead-in phase, a 36 month observational phase (including 9 months of data analysis), followed by a 6 month feasibility phase and a 3 month final analysis phase. A joint data collection instrument will be utilized as part of an Interactive Research Project Grant to collect data on nutritional and outcome parameters in ARF patients. Additional measurements of markers of catabolism, and both biochemical and body composition nutritional parameters, will be made at the principal nutrition sites. The feasibility of implementing an optimized nutritional regimen and measuring the effects on nutritional and metabolic parameters will also be performed.