Encouraged by the results with radiation genetics, the editors of this volume have tried since 1963 to organize a team of scientists in Heidelberg who would examine the problem of chemical mutagenesis in mammals with a variety of methods. Meanwhile, other organizations have also become interested in this problem and various teams, particularly in the U.S.A., but also in West Germany, are working in this field. This development is very auspicious; the spectrum of our methods does permit limited conclusions as to the mutagenic effects of chemical substances in mammals, but we are still far away...