The essential and critical role of inorganic phosphate has been known in veterinary medicine and experimental research on animals for decades. However, only recently has the phosphate depletion syndrome found widespread attention by clinicians. Hypophosphatemia is usually observed in the following clinical situations:chronic alcoholism, recovery phase of diabetic ketoacidosis, administration of phosphate-free solutions in parenteral nutrition, severe respiratory alkalosis, and infusion of fructose. Disturbed organ function in hypophosphatemia is the result of a depletion of inorganic phosphate in the cytoplasm of somatic cells. Such phosphate depletion may be due to either of the following mechanisms or a combination of both. (1) Negative external phosphate balance resulting from phosphate loss in urine or feces or (2) translocation of phosphate from the extracellular into the intracellular space with or without concomitant negative external phosphate balance. In principle, phosphate depletion interferes with the function of all somatic cells. In acute phosphate depletion, the clinically most important disturbances are observed in striated muscle (rhabdomyolysis with myoglobinuric acute renal failure), heart muscle (acute heart failure), and hematological systems (hemolysis, disturbed leukocyte and thrombocyte functions). In contrast, in chronic phosphate depletion skeletal abnormalities (osteomalacia) predominate. Organ disturbances are thought to result from diminished synthesis of ATP and other organic phosphate esters and/or from hypoxia secondary to changes in erythrocyte 2,3-DPG.