Publisher Summary This chapter consolidates and quantitates some deleterious effects of cancer chemotherapeutic agents in humans—namely, their ability to induce chromosomal aberrations, their antifertility effects, their ability to produce congenital malformations under certain conditions, and their carcinogenic potential when used to treat neoplastic and nonneoplastic diseases. It discusses the three classes of antitumor compounds: alkylating agents, antimetabolites, and antitumor antibiotics. These compounds have been extensively studied in vitro and in vivo and they induce chromosomal aberrations; these abnormalities vary according to the agent and the test system used. Combinations of agents or agents plus irradiation also produce cytogenetic damage in human cells. It also provides information on the possible adverse effects of the antimetabolites, antitumor antibiotics, and miscellaneous synthetic agents on spermatogenesis. The current evidence indicates that these effects are related to the dose and duration of chemotherapy, both for single alkylating agents and for combination chemotherapy in which the alkylating agent is one of the components. Anticancer drugs other than the alkylating agents should be more thoroughly studied for possible effects on the fertility in the human female.