Female reproductive functions improve after puberty to reach a maximum within the first quarter of the lifespan of most mammals. Thereafter, there are progressive declines with age leading in most mammalian species to a loss of fertility by midlife. The changes are complex and there can be extensive variations in their timing among individuals, even in inbred rodents. Three markers of reproductive function, length of ovulatory (or estrous) cycles, infertility, and fetal abnormalities, are extensively utilized to monitor reproductive senescence and may be equally valuable in assessing the potential toxicity of xenobiotic agents. The article describes the parameters used to evaluate reproductive function and normal changes with age. In addition, two paradigms that disrupt normal reproductive function in young mature rodents will be briefly described as useful models for analysis of reproductive toxicity. (Copyright (c) 1988 Pergamon Press plc.)