Extensive investigations with mice on the effects of various physical and biological factors, such as dose rate, sex and cell stage, on radiation-induced mutation have provided an evaluation of the genetics hazards of radiation in man. The mutational results obtained in both sexes with progressive lowering of the radiation dose rate have permitted estimation of the mutation frequency expected under the low-level radiation conditions of most human exposure. Supplementing the studies on mutation

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... requency are investigations on the phenotypic effects of mutations in mice, particularly anatomical disorders of the skeleton, which allow an estimatio.. of the degree of human handicap associated with the occurrence o£ parallel defects in man. -Estimation of the genetic risk from chemical mutagens is much more difficult, and the research is much less advanced. Results on transmitted mutations in mice indicate a poor correlation with mutation induction in non-mammalian organisms. On the one hand, mice show little or no mutagenic response to several compounds that are highly mutagenic in other systems. On the other hand, recent results with ethylnitrosourea show that a single injection of 6 mg per mouse of this compound induces a mutation rate 75,000 times greater than that considered as a maximum permissible level of risk from a whole year of exposure to radiation. Further investigation in mice is obviously needed, not rcial orodu T necessarily c