Using the basic records and coded data on magnetic tape, and supplementing both by data received for subsequent calendar years (1972 onwards) under the research program (Menstruation and Reproduction History, MRH) conducted continuously by the principal investigator since 1934, this application proposes to define statistically the beginning years (post-menarcheal) and terminal years (pre-menopausal) of human menstrual experience. Menstrual interval, duration of flow, and spottings as recorded prospectively (i.e. when they occur) will form the major variables. All analyses of all individual histories pre-menopause will be used to develop a criterion for the approach of menopause applicable to the individual. Segregation of histories in which hormonal therapies were used to alleviate menopausal discomfort, and of histories including surgery for tubal ligation, will permit limited description of subsequent effects of these procedures.