Exchange-rate based stabilizations, while useful in accelerating the disinflation process, typically lead to overvalued exchange rates and large current account deficits. These factors, in turn, make it difficult to sustain exchange rate pegs, placing heavy demands upon monetary policy to sustain exchange-rate based programs in their later phases. This paper evaluates the extent to which Mexican monetary policy in 1994 may have loosened, or not tightened sufficiently, in the lead up to the devaluation of the peso that December. Using econometric models of the demand for money, we find evidence that the high growth of the monetary base in 1994 reflected strong positive shocks to the demand for money, not to its supply. Next, we estimate a monetary policy reaction function for Mexico. Based on this estimate, we argue that interest rates rose only moderately less in 1994, in response to downward pressure on the peso and on international reserves, than was predicted by the authorities' reaction function. This result is qualified somewhat by our finding that if interest rates are modeled as reacting to reserves net of Tesobonos, rather than gross reserves, the measured deviation of actual from predicted interest rates would have been much greater. However, the relative complacency with which both the authorities and the market viewed the build-up in Tesobonos, at least until late in 1994, suggests that the reaction function based on net reserves probably does not capture "normal" monetary policy behavior. Our findings suggests that in order to have maintained the peg, the authorities would have needed to intensify their response to exchange market developments--that is, to alter their reaction function--at a time when concerns over the health of the banking sector, and of the economy more generally, would have pointed to a relaxation of monetary policy. Insofar as such tightenings of monetary reaction functions are difficult to achieve, Mexico's experience suggests that policymakers relying on the exchange rate as a nominal anchor probably should be prepared either to abandon that anchor or tighten monetary policy well before speculative pressures intensify
