Aspects of the Problem.- 1. Biochemical Mechanisms of Mutation.- 2. Spontaneous Mutation in Man.- 3. Mutagenic Substances in the Human Environment.- Research Methods.- 4. The Dominant Lethals: Method and Cytogenetic Examination of Early Cleavage Stages.- 5. The Multiple Loci Method.- 6. Evaluation of Presumed Dominant Skeletal Mutations.- 7. Histological and Cytogenetic Investigation Methods on Mammalian Spermatogenesis.- 8. Cytology and Timing of Meiotic Stages in Female Germ Cells of Mammals and Man.- 9. The Effect of Chemical Mutagens on the Mitotic Chromosomes of the Mouse, in vivo.- 10. Investigation of Bone Marrow Smears.- 11. Chromosome Aberrations in Plants.- 12. Possibilities and Limitations of Chromosome Treatment in vitro for the Problem of Chemical Mutagenesis.- 13. Point Mutations in Mammalian Cell Cultures as Measures for Mutagenicity Testing.- 14. Cytogenetic Analysis of Ascites Tumour Cells of Mice in Mutation Research.- 15. The Host-Mediated Assay, a Practical Procedure for Evaluating Potential Mutagenic Agents.- 16. The Internal Level of Mutagens in Mammals.- 17. Biochemical Analysis on Genetically Different and Altered DNA: Methods and Limitations.- 18. The Induction of Extrakaryotic Mutations.- Findings and Application.- 19. The Activity of Alkylating Agents. I. Sensitive Mutable Stages in Spermatogenesis and Oogenesis.- 20. The Activity of Alkylating Agents. II. Histological and Cytogenetic Findings in Spermatogenesis.- 21. Chromosomal Aberrations Induced by Antimetabolites.- 22. Mutagenicity Experiments with Mice and Human Cell Cultures: Treatment with an Acridine Derivative (Trypaflavin).- 23. The Treatment of Human Chromosomes in vitro: Results.- 24. The Problem of Caffeine Mutagenicity.- 25. The Failure of Caffeine to Induce Mutagenic Effects or to Synergize the Effects of Known Mutagens in Mice.- 26. Virus-Induced Chromosomal Alterations in Mammals and Man..- 27. Statistical Examinations in Human Populations.- 28. Monitoring of Human Populalcë