Urea is a nitrogenous compound excreted in the urine by humans and most other mammals. The chemical structure of urea is H₂N- C(_o)-NH₂. Urea is a colorless solid with a melting point of 270.8°F (132.7°C), possessing good solubility in both water and ethanol. A product of protein metabolism, urea is formed by the liver primarily from the ammonia that results when excess amino acids are deaminated (or broken down). In this process--basically, splitting off the amino acid's amine group--the resting ammonia is either used to make other nitrogen-containing compounds or transported to the liver, where it is converted to urea and then excreted by way of the urine.

Urea was first discovered in the urine in 1773 by the French chemist Jean Rouelle. Over 50 years later, in 1828, it was synthesized by the German chemist, Friedrich Wöhler--a feat more remarkable than it sounds. In the early 1800s, it was widely believed that an organic compound like urea--a product formed by the human body itself--could not be manufactured in the laboratory as though it were a common chemical. When Wöhler accidentally found he had synthesized crystals of urea while evaporating a solution of ammonium cyanate, he was surprised that it was possible. In his excitement, he dashed off a letter to his friend, the famous Swedish chemist Jöns Berzelius, and declared, "I can make urea without needing a kidney, whether of man or dog!" Wohler's historic preparation of "artificial" urea demonstrated to the scientific world that an organic compound could be synthesized, not only by a living organism, but by the working chemist. For many, then, Wöhler is considered the true father of organic chemistry.