As editor I want especially to thank Dr. Ernst Freese for helpful co­ operation in preparing these volumes, and to express my appreclatlOn to Drs. Kurt Hirschhorn and Marvin Legator, the other members of the editorial board. Alexander Hollaender January 1971 Preface The purpose of these volumes is to encourage the development and ap­ plication of testing and monitoring procedures to avert significant human exposure to mutagenic agents. The need for protection against exposure to possibly mutagenic chemicals is only now coming to be generally realized. The recently issued Report of the Secretary's Commission on Pesticides and Their Possible Effects on Health (the Mrak Report-U.S. Department of Health, Education and Welfare, December 1969) has made an important start. Its Panel on Mutagenicity recommends that all currently used pesticides be tested for mutagenicity in several recently developed and relatively simple systems. Whether recommendations such as these are actually put into effect will depend on convincing government, industry, and the public that the problem is important, that the proposed tests would be effective, and that they can be conducted at a cost that is not prohibitive. Why is it important to screen environmental agents for mutagenic activity? To those who will read this book, the answer is self-evident. The sine qua non of all that we value and all that we are is our genetic heritage.