Adenosine is a purine nucleoside present in every cell of the human body. It is released into the extracellular space under physiologic and pathophysiologic conditions characterized by increased oxygen demand:supply ratio. Adenosine can exert a wide spectrum of effects in various organs and tissues. Exogenous adenosine has a wide spectrum of effects in experimental animal models as well as humans. The pharmacokinetics, pharmacodynamics, and the interaction of adenosine with other drugs are reviewed.