Urine has long fascinated medical minds. As a folk remedy, urine has been used as a mouthwash, toothache treatment, and a cure for sore eyes. Hippocrates (460-377 B.C.) was the first to observe that the condition of the urine can reflect health, noting that frothy urine denoted kidney disease. During the Middle Ages, health practitioners consulted charts in which certain urine colors were matched to certain diseases. In the seventeenth century, British physicians diagnosed diabetes by having their medical students taste sugar in patients' urine. Today, urine composition is still used as a window on health, and also to check for illicit drug use.

Certain inherited disorders can alter urine quite noticeably. The name maple syrup urine disease vividly describes what this inborn error of metabolism does to the urine. This condition, which causes mental retardation, results from a block in the breakdown pathways for certain amino acids. In alkaptonuria, one of the first inborn errors to be described, urine turns black on standing. This condition also produces painful arthritis and blackened ear tips. People with Wilson disease have an inherited inability to excrete copper. If they are properly diagnosed and given the drug penicillamine, they excrete some of the built-up copper, and their urine takes on a coppery appearance.

Other genetic conditions alter urine without causing health problems. People with beeturia excrete dark pink urine after they eat beets. The problem for people with urinary excretion of odoriferous component of asparagus is obvious. Parents of newborns who have inherited blue diaper syndrome are in for a shock when they change their child's first diaper. Due to a defect in transport of the amino acid tryptophan in the small intestine, the infant's urine turns blue when it hits the air. Bacteria degrade the partially digested tryptophan, producing a compound that turns blue on contact with oxygen.

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