This thesis analyzes the effect of corporate tax rates on the purchasing-power-parity (PPP) doctrine. The data used to test this hypothesis are drawn from the U. S., the U. K., the Federal Republic of Germany, Canada, and Japan. The first chapter introduces the reader to the concepts of the PPP doctrine and states the hypothesis. Chapter 2 reviews the literature on the PPP doctrine. Chapter 3 specifies a model of the PPP doctrine including tax rates. Chapter 4 reports and interprets the findings. The study is summarized and conclusions are drawn in chapter 5. In this study it is shown that tax rates are significant only in the case of the U. S. dollar/Canadian dollar exchange rate.