Objective To observe the relationship between serum creatine kinase isoenzyme MM sub-bands (CKMM3/MM1 ratio) and the gradation of coronary stenosis and provide a simple, reliable, and economical method for identifying high-risk unstable angina pectoris (UAP). Mehtods Blood samples were drawn at different time after onset of chest pain in 21 patients with UAP and only once in 20 each volunteers for control. CKMM3/MM1 ratio was detected by nonserial buffer agarose gel electrophoresis. CKMB and CK were observed by velocity method. An emergent coronary arteriography was performed as soon as patients were admitted into hospital. Results Patients with UAP were divided into two subgroups:patients with elevated serum enzyme [P( + )] and patients with normal serum enzyme [P( - ) ] according to CKMM3/MM1 ratio ＜ 0.5. Patients with UAP(+)had higher serum CKMM3/MM1 ratios from 0.5 to 12hrs and serum CKMB from 2 to 12 hrs than those with UAP( - ) and control ( P ＜ 0.05) . Serum enzyme concentrations of patients with UAP whose coronary lumen had 90％ or more than 90％ stenosis were significantly higher than those whose coronary lumen had less than 90％ stenosis (P＜0.01) . AnyCKMM3/MM1 ratio was less than 1.0 and CK within the normal range in patients with UAP( + ) group. Conclusions CKMM3/MM1 ratios in patients with UAP can reflect severity of myocardial ischemia. Serum CKMM3/MM1 ratio provides a simple, reliable, and economical method for identifying high-risk UAP.