Syncope is a transient loss of consciousness, which is the result of global brain hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete resolution. Syncope is a common clinical problem due to its complex, multi-causal etiology, not completely understood pathogenesis and potential complications. Diagnosis of syncope is often associated with the implementation of many medical tests. In the recent years, the role of determining the concentration of NT-proBNP in the differential diagnosis of syncope has been highlighted. Aims of the study was analysis of NT-proBNP concentrations in patients with cardiogenic syncope in comparison to patients with neurogenic syncope and determination of the threshold value of NT-proBNP to differentiate cardiac and neurogenic syncope and to determine its sensitivity and specificity. The study included 160 pts (64 man, 96 women), aged 18 - 77 yrs (mean age 50,6) with a reflex syncope (group I) or cardiac syncope (group II). To determine the etiology of syncope, collected were: medical history for symptoms and circumstances of the syncope, measurements of blood pressure, resting ECG recording, cardiac echocardiography, and the concentration of NT-proBNP levels. Results: the group I included 80 pts (29 men, 51 women), aged 18 - 72 yrs (mean age 41.2). Group II included 80 pts (35 man, 45 women), aged 38 - 77 yrs (mean age 62.1). The assessment of concentrations of NT-proBNP showed significantly higher levels in group II than group I (467.6 +/- 227.4 vs 64.1 +/- 59.1; p <0.0001). In patients with arrhythmias and conduction abnormalities, the levels of NT-proBNP were higher in comparison to those without such disorders (364 +/- 249 vs. 171 +/- 209 pg/ml, p < 0.001). It was found that the concentration of NT-proBNP at 230.6 pg/ml might be a cut-off point that allows the prediction of cardiogenic cause of syncope with 96% specificity, 92% sensitivity and 93% negative predictive value. Conclusions: 1. The concentration of peptide NT-proBNP patients with reflex syncope. 2. It was shown that the cut off concentration of the NT-proBNP equal 230.6 pg/ml is characterized by the high sensitivity, specificity, and negative predictive value in determining the etiology of syncope.