As a result of the industrial revolution, man's technological achievements have been truly great, increasing the quality of life to almost unimagined proportions; but all this progress has not been accomplished without equally un imagined health risks. Sufficiently diagnostic short-term assay procedures have been developed in recent years for us to determine that there are mutagenic agents among thou- sands of chemicals to which the human population is exposed today. These chemicals were not significantly present prior to the indus- trial revolution. As of today, there are no procedures available which have been adequately demonstrated to assess individual sus- ceptibility to genotoxic exposures, and as a result we have had to rely on extrapolating toxicological data from animal model systems. The question is can we afford to allow such an increased environ- mental selection pressure via mutagenic exposures to occur without expecting adverse long-term effects on our health. It is apparent from this line of reasoning that what is lacking and immediately needed are test procedures that can be applied to humans to assess genotoxic exposure as well as individual susceptibility to it. There have already been two conferences which have focused at- tention on this research area. "Guidelines for studies of human populations exposed to mutagenic and reproductive hazards" (A. D. Bloom, ed., March of Dimes Birth Defects Foundation, White Plains, New York, 1981) and "Indicators of genotoxic exposure in humans" (Banbury Report 13, B. A. Bridges, B. E. Butterworth, and I. B.