AbstractI would first like to thank the Environmental Mutagen Society for honoring me with its 1980 award; I also would like to take this opportunity to acknowledge all the people who have worked with me and helped me since I started my work in mutagenesis in 1953. I feel especially indebted to my wife, Martha, whose support has been absolutely essential for my career.I would now like to explore some important problems in environmental mutagenesis. Obviously, I cannot touch upon new developments in all aspects of environmental mutagenesis ‐ a field that has become increasingly broad in recent years. As in the past, there continue to be major advances in understanding mechanisms of mutagenesis, developing short‐term tests, characterizing mutations, elucidating the relationship between mutagenesis and carcinogenesis, understanding the metabolism of mutagens, and many other areas. Many of these advances are reflected in the contents of the papers, symposia, and poster sessions of this meeting. In the years that I have been involved in mutation research and environmental mutagenesis, my interests and research activity have spanned a number of these areas; and I am pleased by the recent progress that I see taking place in them. In this talk, however, I would like to direct my comments toward a rather new dimension in environmental mutagenesis in which I have become increasingly interested: The monitoring of mutations in the human population.In the monitoring of the human population there are two choices: We can monitor the progeny of an exposed population or we can consider exposed persons as populations of cells and measure the mutant frequency in individual cells in these persons. Technical developments are advancing rapidly in both of these approaches. The pioneering work of James Neel in measuring germinal effects of mutagens in the human population is well known [Neel, 1970]. Methods for measuring mutation frequencies in single cells in vivo also are beginning to be available. For instance, Strauss and Albertini [1979] are developing a system to detect HGPRT mutants in human lymphocytes. Of course, there are still difficult problems to be resolved in this system; and we do not know with certainty.