Aim. The aim of this study was to evaluate the impact of metabolic syndrome and features clustering in this syndrome on the antiplatelet effect of clopidogrel and aspirin in patients with myocardial infarction.Material and methods. The study population comprised 186 consecutive patients treated with primary percutaneous coronary intervention for acute myocardial infarction. Measurements of ADP induced platelet aggregation (ADP-PA) and arachidonic acid induced platelet aggregation (AA-PA) were performed using impedance aggregometry with a Multiplate Analyser. The following factors were analysed as potential determinants of responsiveness to clopidogrel and to aspirin: diagnosed metabolic syndrome, diabetes, hypertension, abdominal obesity, body mass index (BMI), and serum concentrations of triglycerides, HDL-cholesterol and high sensitivity C-reactive protein (hsCRP).Results. The ADP-PA was significantly higher in patients with metabolic syndrome and with diabetes.The AA-PA was significantly higher in subjects with increased levels of hsCRP and in subjects with BMI > 25 kg/m2. The hsCRP was found to be the only independent factor influencing APD-PA (p=0.034). Serum concentrations of hsCRP, HDL-cholesterol and abdominal obesity were independent factors influencing AA-PA (p=0.000004).Conclusion. Metabolic syndrome, diabetes mellitus, obesity and increased hsCRP are determinants of low responsiveness to aspirin and clopidogrel in patients with ACS treated with PCI