An oral contraceptive containing 20 micrograms of ethinylestradiol and 250 micrograms of levonorgestrel was given to 5 normally menstruating women for two consecutive cycles. Peripheral serum levels of FSH, LH, estradiol-17 beta and progesterone were determined during the treatment period and during two control cycles, one immediately before, and one immediately after treatment. In all 5 women studied there were no LH peaks and no luteal phase levels of progesterone during the treatment cycles indicating complete inhibition of ovulation. 4 of the 5 women showed no biphasic estradiol pattern. Posttreatment control cycles showed reestablished ovulatory pattern in 4 of the 5 subjects.