This study aims to verify statistically, through the utilization of an interest rate covered parity model adjusted to the country-risk and other risks (domestic, mainly), what are the determinants of Brazilian interest rates for long-term public fixed income securities - in this case, the so-called National Treasury Notes - Series F (NTN-Fs) with maturity in approximately 10 years, more precisely, in 2017. The dependent variable was defined as being the yield- to-maturity of the respective NTN-Fs, whereas the independent or explanatory variables were the risk-free rates of the US 10-year Treasuries, the Brazilian country-risk and the exchange rate risk. The other risks (especially domestic ones), as well as they reflect the differential between the NTN-Fs and the other variables, are one of the error term components. Given that the independent variables have strong multicollinearity - which brings biased results to the determination and individual coefficients -, we opted for using a VAR model and, based on it, obtain the endogenous degrees of each variable. Then, it was possible to observe the causality and importance level of the variables individually and if the model was correctly specified - that is, if the long-term NTN-Fs interest rates were in fact explained by the other variables. The main VAR model tools - which are the variance decomposition and the impulse-response functions - allowed us to make important conclusions about the delayed impacts of variations or shocks occurred in the independent variables over the analyzed NTN- Fs interest rates. The results proved that NTN-Fs interest rate is the most endogenous variable of the model and, therefore, the dependent one. The results also showed that the exchange rate risk is the less endogenous variable, suggesting it has a decreasing importance for the long-run interest rate building in Brazil. However, the most important conclusion was the evidence that there is a negative correlation between the risk-free rate and Brazilian long-run securities interest rates, opposing, at least in 2007, the Portfolio Theory, which foresees a positive relationship between the risk-free irate and the return of an asset.