By serial determinations of plasma LH, FSH, progesterone and estradiol-17beta as well as total gonadotropines, total estrogens and pregnanediol in 24 h urine samples it was possible to classify 19 cycles of premenopauseal women, aged 44-50 years, into two groups. The first group showed ovulatory cycles with partially shortened hyperthermic phases in the basal body temperature curves, slightly elevated levels of FSH and diminuished estradiol-17beta, pregnanediol and progesterone concentration, indicating the beginning insufficiency of the ovarian function. The second group was characterized by several times above normal elevated FSH and somewhat less elevated LH levels significantly lowered estradiol-17beta and only basal progesterone and pregnanediol concentrations. The ovulatory transitional cycles explicated a nearly normal fluctuation pattern which was completely abolished in the anovulatory cycles.