ANUMBER of enzymes are known to occur in the body in one or more distinct forms, usually called isozymes.1-3 The molecular basis for this phenomenon is known in the case of two soluble enzymes: creatine kinase and lactic dehydrogenase. In both cases the isozymes are formed of polymers of two kinds of subunits, each of which is under separate genetic control. Both enzymes, more particularly lactic dehydrogenase, have come under intensive investigation in the past few years, in part because of the inherent interest of the phenomenon of isozyme structure, and also because it has been hoped that the pattern of isozymes in a cell would give information or insight of clinical value. This paper reports the isozyme types and normal levels of creatine kinase from human tissues obtained at autopsy. These values are of interest because of the widespread use of serum creatine kinase activity as an indicator