Classically it has been considered that the living organisms in general should confront a setting of metabolic acidosis. This situation was based on the fact that the protein metabolism generated daily an amount of nonvolatile acids. Atkinson and others have showed how bicarbonate is produced after proteins have been metabolized. Because this, living organisms find themselves before the constant risk of metabolic alkalosis. In order to overcome this, the Liver disposes of the proteic bicarbonate through the urea synthesis and the glutamine metabolism. The kidney conserves the bicarbonate that is metabolized In the Liver thanks to the primary need of maintaining a strict hydroelectrolytic balance. Finally, the mechanisms wich allow the liver to become the central organ in acid-based regulation and some pathophysiologic situation that i1ustratethe new model proposed are exposed.