The current state of mutagenicity testing 219 germ cell mutations after chemical exposure (or in fact any agent) is sadly lacking. In industrial areas it is often hard to pinpoint the exact chemical or agent which may be causing the problem. Unbiased abortion rates are difficult to obtain in interview by comparison with control or unexposed populations. Even if they are taken from hospital and medical practitioners' records not all abortions are recorded. Auerbach (106) does not believe that we shall even be able to identify potential human mutagens with complete confidence and even less shall we be able to feel confident about such quantitative features as thresholds, dose-effect curves and comparisons between mutagens in the human environment. She thinks this is unavoidable when we as a species are both the subject and the object of such investigation. However, we do have thousands of untested chemicals in our environment and some attempt must be made to identify those potentially hazardous to man. The limitations of the simple short-term tests which are more concerned with the concept of somatic mutation are becoming better understood and the problem of false positives and negatives has been discussed earlier (8). At present, we can only do our best with the test systems available and hope that as research progresses our understanding and techniques will improve so that results generated in our model systems will become unequivocal in terms of hazard to man. To achieve this goal, attention will have to be given to studies aimed at assessing the significance to man of positive mutagenic responses produced by a test system for a given chemical, in addition to the search for better assay procedures. ACKNOWLEDGMENTS The author wishes to thank Professor P. Oftedal, Department of Genetics, University of Oslo, and Drs J. A. Styles and J. Ashby, of this laboratory, for reading the manuscript and offering helpful comments. REFERENCES 1 Ames, B. N., Lee, F. D. and Durston, W. E. An improved bacterial test system for the detection and classification of mutagens and carcinogens. Proc. Nat. Acad. $ci. (USA). 70 782-786 (1973). 2 Ames, B. N., Durston, W.E., Yamasaki, E. and Lee, F. D. Carcinogens are mutagens:a simple test system combining liver homogenates for activation and bacteria for detection. Proc. Nat. Acad. Sci. (USA) 70 2281-2285 (1973). 3 Ames, B. N., McCann, J. and Yamasaki, E. Methods for detecting carcinogens and mutagens with the Salmonella/mammalian microsome mutagenicity test. Mutation Res. 31 347-364 (1975). 4 McCann, J., Spingarn, N. E., Kobori, J. and Ames, B. N. The detection of carcinogens as mutagens: bacterial tester strains with R factor plasmids. Proc. Nat. Acad. $ci. (USA) 72 979-983 (1975). 5 McCann, J., Choi, E., Yamasaki, E. and Ames, B. N. Detection of carcinogens as mutagens in the $almonella/microsome test. Part I, Assay of 300 chemicals. Proc. Nat. Acad. Sci. (USA) 72 5135-5139 (1975). 6 McCann, J. and Ames, B. N. Detection of carcinogens as mutagens in the Salmonella/microsome test. Assay of 300 chemicals. Part II. Proc. Nat. Acad. $ci. (USA) 73 950-954 (1976). 7 Coombs, M. M., Dixon, C. and Kissonerghis. Evaluation of the mutagenicity of compounds of known carcinogenicity belonging to the benz[a]anthracene, chrysene and cyclopenta[a]phen- anthrene series, using Ames's test. Cancer Res. 36 4525-4529 (1976). 8 Purchase, I. F. H., Longstaff, E., Ashby, J., Styles, J. A., Anderson, D., Lefevre, P. A. and West- wood, F. R. Evaluation of six short-term tests for detecting organic chemical carcinogens and recommendations for their use. Nature 264 624-627 (1976). 9 de Serres, F. J. The utility of short-term tests for mutagenicity in the toxicological evaluation of environmental agents. Mutation Res. 33 11-15 (1975).

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