This study aims to verify statistically, through the utilization of an interest rate covered parity model adjusted to the country-risk and other risks, what are the external determinants of daily Brazilian domestic in- terest rates for long-term public fixed income securities â in this case, the so-called National Treasury Notes - Series F (NTN-Fs) with maturity in 2017. The dependent variable was defined as being the yield-to-maturity of the respective NTN-Fs, whereas the independent variables were the risk-free rates of the US 10-year Trea- suries, the Brazilian country-risk and the exchange rate risk. Given that the independent variables have strong multicollinearity, we opted for using a VAR model and, based on it, obtain the endogeneity degree of each variable. The main VAR model tools â which are the variance decomposition and the impulse-response func- tions â 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 the exchange rate risk is the least endogenous one. The most important conclusion was the evidence that there was a negative correlation between the risk-free rate of the US 10-year Treasuries and Brazilian long-run securities interest rates in 2007, opposing the previous expectation that there would be a positive relation between these variables.