The assay for the MB isoenzyme of creatine kinase is widely used in the diagnosis of acute myocardial infarction. Patients with metastatic carcinoma of the prostate may have an elevated serum creatine kinase BB fraction, which by immunoinhibition method may be read mistakenly as creatine kinase MB. We report the case of a patient with a history of myocardial injury, chest pain, total CK above of reference range and CK-MB isoenzyme, determinated with an immunoinhibition technique, larger than 100% of enzymatic activity of total CK, that was carrier of a prostatic adenocarcinoma in stage D2. We comment the diseases in which the CK-BB fraction may be elevated, discuss the laboratory methods for the determination of creatine kinase isoenzymes, and revised, briefly, the properties of the new immunoassays, that measure mass concentration of creatine kinase MB, in the diagnosis of acute myocardial infarction.