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The aim of this paper is to analyse the adjustment process of real effective exchange rates towards their equilibrium level for the cfa zone countries over the period 1985-2007. Accordingly, we estimate a panel smooth transition error correction model in order to take into account non-linear phenomena. In particular, we show that the adjustment process of real effective exchange rates is indeed asymmetric while this asymmetry differs substantially between countries. This last result tends to show the difficulty to apply a single exchange rate policy in the cfa zone and rather calls for further coordination and policy harmonization between the countries of the zone. Classification JEL: C23, F31, O1