Abstract: Objective: To discuss the cause of false increase in serum MB form creatine kinase (CK-MB) activity in non-cardiogenic patients and its relationship to the disease.Methods: The creatine kinase isoenzyme in the routine specimen of 55 patients whose CK-MB activities were higher than the reference level (25 U/L) and the ratio to creatine kinase (CK) were more than 0.38 were determined using agarose gel electrophoresis.One week later,the CK-MB was determined again and the results were compared with the original values.The analysis was performed combining the clinical diagnosis results.Results: Forty-one of the 55 patients was diagnosed as malignant tumors (16 liver cancer,11 lung carcinoma,7 prostate carcinoma,7 other tumors) and 12 patients as liver cirrhosis;Creatine kinase isoenzyme and the contents of CK-MB of the patients were all less than 5%;Macro-CK2 was detected in 34 cases of malignant tumors,and CK-BB was detected in 23 cases of malignant tumors.Both macro-CK2 and CK-BB were detected in 16 cases of Malignant tumors;Macro-CK2 was detected in 12 cases of liver cirrhosis.Comparison was made between the CK-MB active concentrations detected in the two times.No significant variation was observed (P>0.05).Conclusions: The false increase in serum CK-MB activity is mainly caused by the abnormal increase of CK-BB or macro-CK (macro-CK1,macro-CK2) in blood;their appearance is closely related to liver cirrhosis and certain malignant tumors.