The amino acid L-arginine is an essential amino acid for cats. It is converted to the amino acid citrulline in the intestines. Citrulline is then re-converted back to L- arginine by the kidneys, the main location of arginine synthesis in cats. L-arginine is a precursor for nitrous oxide (NO) synthesis in the cat kidney. NO is believed to play a crucial role in regulating blood flow through the kidney. Studies have shown that cats with naturally occurring chronic renal failure have decreased levels of L-arginine. It is hypothesized that increasing blood levels of arginine will increase NO production in the kidney and have a beneficial effect on feline kidney disease. No studies have been conducted to determine the safety of oral supplementation of L-arginine in cats with chronic renal failure or if oral supplementation can increase arginine blood levels. In this pilot study, 12 cats with kidney disease will be supplemented orally with either L- arginine or a placebo over a one month period to determine the safety of supplementation and whether increased blood levels of arginine can be achieved. If safe and effective at increasing blood arginine levels, then larger studies would be warranted to determine if survival and quality of life would be improved in cats with chronic renal failure.