Creatine kinase (CK) catalyzes the reversible transfer of the phosphoryl group from phosphocreatine to adenosine 5'-diphosphate (ADP), thus regenerating adenosine triphosphate (ATP). Creatine kinase genes are expressed in several tissues with high, fluctuating energy turnover, e.g. skeletal and cardiac muscle, brain and photoreceptor cells, and spermatozoa. Several isoenzymes of CK have been characterized: brain-type, muscle-type, and the hybrid isoenzymes, as well as the mitochondrial CK isoenzymes. Measurements of serum CK is a routine test in the diagnosis of acute myocardial infarction and various muscle disorders. Elevation of the serum CK level in psychiatric patients is a fairly nonspecific phenomenon. Most commonly, an elevated serum CK level is due to intramuscular injections, use of restraints or other intense isometric activity. Although it is still controversial, increased CK activity is one of basic criteria of neuroleptic malignant syndrome. Despite many studies on the importance of CK in postnatal brain and pathogenesis of psychiatric disorders, its role in psychiatry remains still mysterious.