Treatment and survival of reproductive-age patients with chemotherapy raises the question of possible effects on procreative ability. An attempt has been made to establish an animal model system. The anticancer agents nitrogen mustard and procarbazine caused decreased fertility in mice of both sexes and induced meiotic chromosomal abnormalities, at least in the male. Progeny of treated mice showed similar meiotic chromosomal changes. The possibility of similar effects in human beings receiving chemotherapy must be considered.