BACKGROUND Macro CK (creatine kinase) as a reason for high CK values has been known since 1979. Even in the era of troponin determination for the diagnosis of myocardial infarction, an elevated CK value can still cause confusion, especially as CK-MB rises earlier than troponin. The case report should remind us of this often forgotten differential diagnosis of elevated CK. CASE REPORT A 73-year-old patient was treated with leuprorelin hormone therapy for prostate cancer (stage pT1c G2). In addition, he received percutaneous radiation therapy of the prostate and high-dose-rate brachytherapy twice with 10 Gy each. Close to 1 year later, he complained for the first time of dyspnea on exertion and thoracic tightness. Serum CK was 232 U/l, and CK-MB 62 U/l, which was confirmed by several controls. Troponin T test was negative, and GOT, GPT, LDH, and PSA were all within the normal range. Acute myocardial infarction was ruled out on clinical grounds and by six sequential ECGs. Subsequently, the patient remained without further cardiac complaints and in good condition. Isoenzyme electrophoresis finally solved the problem and revealed CK-BB-IgG complex type 1 (macro CK-1). CONCLUSION High CK-MB values in cardially healthy patients should remind us of the possibility of macro CK which is seen in approximately 0.5% of cases and should be included in the differential diagnosis.