The present work looked for to show the influence of nominal variable in the determination of nominal exchange rate R$/USS. For this, the model of the parity of the tax of interests was used, ally to the monetary market. It was looked, also, to foresee the tax of exchange rate R$/USS, until December of 2005. For reaching such objectives, the equations of the system had been obtained by the Vector Error Correction Model (VECM). The results had shown that the nominal variable are very important to determinate the exchange rate and that the model of parity of the tax of interests, ally to the monetary market is confirmed for the Brazilian case in the period of analysis (jan/1999 to dez/2004). This conclusion is made on the basis of the high capacity of forecast of the model structuralized for the development of the study. Admitting the forecasted values, the exchange rate presents a light trend of fall until December of 2005, closing in 2,45 R$/US$.