Purchasing power parity has been the subject of many empirical studies. Much of this work has focused on recent history in developed countries. This article reports results of tests for nonlinear, mean reversion of the real exchange rate for a less-developed country, Mexico, using a previously unexploited data set of monthly observations for 1930-1960. The test results provide limited support for Purchasing Power Parity (PPP). © 2011 Taylor & Francis.