The changes in serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FHS), estradiol, and progesterone that occur both early and late in reproductive life were characterized and compared with findings in young, normal women and in patients with certain menstrual disorders. A total of 50 complete menstrual cycles in 37 were examined. Five distinct patterns of hormonal regulation were found, three of which are reported here: (a) A long follicular phase and delayed follicular maturation in young women with long, unpredictable intermenstrual intervals from menarche; (b) a short follicular phase with increasing age and in short cycles in perimenopausal women; and (c) true anovulatory vaginal bleeding in long cycles in perimenopausal women. The short cycles before and during the menopausal transition were found to have lower E2 levels and high FSH concentrations throughout, while LH remained in the normal range. During long cycles in perimenopausal women, concentrations of LH and FSH were in the menopausal range. However, follicular maturation was observed months after high levels of gonadotropins were attained. These studies permit the characterization of the menstrual history of the normal woman in terms of the hormonal changes that occur and provide a basis for the definition of several disorders of follicular maturation.