This volume, based on the International Congress Creatine: From Basic Science to Clinical Application, held in Milan on June 4, 1999, outlin es the physiological role of creatine in the human body as well as its possible role in different pathological conditions. Creatine is alrea dy used as a dietary supplement to augment muscle performance in healt hy individuals and inpatients with immobilizing diseases, such as comp lex fractures. There is also an increasing interest in its administrat ion in a growing number of clinical conditions. A specific deficit of endogenous synthesis of creatine which responds to high dosage exogeno us supplementation has been described. In cardiac failure and in chron ic obstructive pulmonary disease, creatine improves the contractility of the muscular system. Promising effects of this substance have also been described in animal models of neurodegenerative disorders, such a s amyotrophic lateral sclerosis, and in some mitochondrial cytopathies .