Relevance of the carcinogenic effects of anticancer agents has arisen in the context of three circumstances: (a) when patients who have a favorable outlook without treatment receive chemotherapy, (b) when several alternate therapies with varying carcinogenic potential are available, and (c) when considering the introduction of a new drug into clinical investigation and/or clinical practice. Teratogenic effects require special attention when dealing with women in their reproductive years. Techniques to evaluate the mutagenic effects have opened up new areas of research and will be increasingly applied to the study of anticancer drugs.