A rapid and sensitive method of isoforms of CK (EC 2.7.3.2) -MM in human serum by chromatofocusing was reported. The assay system involved Mono P (HR5/20) column. fast protein liquid chromatography (FPLC) system and post column reactor. The result of CK-MM isoforms was obtained within 40 min after serum application to equilibrated column.The lower limit of sensitivity for CK activity is 8U/L and the linear capacity is 17-2085U/L, with CV values of 2.1%. 2.7% and 11.0% for MM₁. MM₂ and MM₃ respectively.