A modified procedure is developed for estimation of creatine phosphokinase (CPK) isoenzymes in blood serum. The method is used for diagnostics of early steps of myocardial infarction. The procedure is based on electrophoretic separation of CPK isoenzymes by means of Soviet equipment and acetate cellulose films manufactured by the Institute of Synthetic Resins in Vladimir. Similar data were obtained with the acetate cellulose films provided by 'Helena' USA. The procedure may be recommended as a standard one for clinico-diagnostic laboratories specialized in cardiology.