Acute renal failure (ARF) is characterized by a persistently high mortality rate, mainly in prerenal, postaggressive forms. Nutritional perturbations are related to the metabolic response to stress, ie mainly an elevation of the basal caloric expenditure and a marked proteic hypercatabolism, and to specific consequences of the loss of renal function. Identification of characteristic metabolic patterns and of their mediators, leading to a nutritional support adjusted to the elevated demand rather than to the impairment of renal excretion faculties, may improve the prognosis. Benefits of such a nutritional support may be restricted to hypercatabolic forms of ARF in the intensive care unit, provided extrarenal failures are reversible.