The valuation of the real exchange can lead dficits not sustainable in the current accounts, indicating the necessity of exchange readjustments; to the measure that the speculators take conscience of that, or potential a banking crisis, or a contraction of great depth, inhibits the authorities to raise the taxes of interests, finishes recognizing the biggest probability of success in case of a speculative attack (KRUGMAN, 2001). According to Kaminsky, Lizondo and Reinhart (1998), the valuation of the real exchange is one of more efficient the antecedent pointers to detect the risk of an attack especulativo.2.2 the Regimen of Exchange Perhaps FlutuanteO floating exchange regimen is adjusted for developed economic markets and steady, not being toa that the biggest countries of the world use this system, where the value of the national currency is stipulated by how much the purchasers they are made use to pay for it. Such aspect is determined by offers and demand that, in turn, is determined by the foreign investment, taxes of importation and exportation, inflation and a set of other economic factors. According to Gordon (2000), the regimen of flexible exchange can be ' ' limpo' ' or ' ' sujo' ' , depending on the intervention level of the government in the exchange taxes. The system of exchange tax ' ' limpo' ' he is that one that is pure, without no intervention of the central bankings, whereas in an exchange system ' ' sujo' ' , the government, through its Central banking, does not allow that the national currency floats with total freedom, using itself of intervention to prevent that the currency is depreciated in the international market beyond a definitive platform. When ' is identified to fluctuations; ' above-normal ' ' in the quotation of foreign currency, as much for top how much for low, the Central banking enters in action as buying or selling, to tranquilize the operators of exchange how much to the normality of the situation.