Recent studies in humans have demonstrated the importance of the kidney in amino acid metabolism. In particular, it has been shown that conversion of phenylalanine to tyrosine occurs in the kidney and at a rate similar to that of the liver. Furthermore, unlike the liver, the kidney releases more tyrosine than it produces. In this review, the importance of this metabolic role of the kidney is discussed in context of chronic renal failure. The effect of renal failure on skeletal muscle protein metabolism is also discussed.