Creatine phosphokinase, also called creatine kinase, is found primarily in the cytoplasm and mitochondria, and both decreases and increases are not normal. Creatine kinase is found primarily in skeletal, cardiac, and smooth muscle, and also in small amounts in brain tissue, the gastrointestinal tract, the lungs, and the kidneys. Creatine kinase is one of the more important kinases that enable intracellular energy conversion as well as muscle contraction. A decrease in creatine phosphokinase is considered to be hyperthyroidism, and the increase is categorized into physiologic and pathologic increases. Physiologic increases are common after strenuous exercise, in pregnant women, and in newborns, where creatine kinase activity is also higher. Pathologic increases are considered in myocardial infarction, viral myocarditis, myotonic dystrophy, pericarditis, and cerebrovascular disease. If creatine kinase is elevated or lowered, the cause should be identified and treated.