Ovarian function (encompassing the cyclical production of estrogen and progesterone during the reproductive years and the timing of ovarian failure or menopause) plays an important role in women's health. Menstrual cycle patterns may reflect hormonal status, and specific menstrual characteristics such as cycle length or variability may directly or indirectly affect the risk of developing hormonally-mediated diseases such as osteoporosis. Menopause represents a normal aspect of aging, but it also influences risk for a wide variety of diseases. Studies have reported increased mortality risk with early natural menopause, and age at menopause has been proposed to be a marker of aging and health. The causes and consequences of early menopause is another important focus of this project. Potential endocrine disrupting chemicals are particularly relevant to the mission of NIEHS, and this project incorporates the study of such exposures. The specific studies that have been completed or are currently underway within this project include: 1) Menstrual Cycle Patterns in Relation to Risk of Chronic Diseases - analyses using prospectively collected menstrual cycle data from over 800 women followed from their 20's through menopause. The specific health conditions examined in relation to menstrual cycle patterns include heart disease, diabetes, perimenopausal fracture risk and total mortality. 2) Menopausal Status and the Menopausal Transition - analyses using national population-based studies (the National Health and Nutrition Examination Survey III and the National Health Information Survey), including methodologic research comparing different analytic methods for assessing associations with timing of menopause. 3) Pesticide Exposure, Menstrual Cycle Characteristics and Timing of Menopause - analyses using the Collaborative Perinatal Project, the Agricultural Health Study, and a newly-designed longitudinal study examining biological measures of DDE and PCB exposure in relation to timing of natural menopause This third set of studies was prompted by the recognition of the endocrine disrupting and ovotoxic potential of specific pesticides. a topic of particular interest to NIEHS. Despite the evidence from toxicology studies, there has been little effort on the part of epidemiologic studies to examine the ovarian-related effects of organochlorines and other environmental contaminants.