In this study, we investigated the influence of two combined oral contraceptives on pituitary gonadotropin secretion and their pulsatile characteristics. The contraceptives compared were 30 micrograms ethinyl estradiol plus 125 micrograms levonorgestrel; and 20 micrograms ethinyl estradiol plus 150 micrograms desogestrel. In 13 healthy normocyclic women, hormonal patterns were obtained in the early follicular phase (EFP) and mid-luteal phase (MLP) of an ovulatory control cycle, and on day 5/6 and day 20/21 of the first treatment cycle during a 12-hour period of continuous blood sampling. On the fifth day of treatment, both combinations had significantly suppressed the mean levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The LH pulse frequency of the treatment cycle was significantly inhibited in comparison with the EFP of the control cycle. While increased LH pulse amplitudes were observed on treatment day 5 for both combinations, only the effects of the levonorgestrel-containing combination were found to be significant. In all volunteers, ovulation was reliably inhibited during the treatment cycle, which was indicated by very low progesterone levels. Estradiol secretion was also suppressed on treatment day 21. It is concluded that: (1) the pulsatile character of gonadotropin secretion is maintained at a low level during treatment with low-dose contraceptives; (2) the effects of the monophasic combinations on gonadotropin pulsatility do not seem to depend on the amount of ethinyl estradiol they contain.