Adenosine 5’-triphosphate (ATP) is a naturally occurring nucleotide present in every cell of the human body. Although ATP is known primarily for its role in intracellular energy metabolism, it also is widely distributed outside the cell. Extracellular ATP and its breakdown product, adenosine, are involved in the regulation of numerous biologic processes. ATP is the energy that drives cell activity, and energy intake from food ultimately is transformed to ATP.