In order to improve the ovarian response to exogenous gonadotropins and to reduce the risk of the ovarian hyperstimulation syndrome and of multiple pregnancies, human menopausal gonadotropin (hMG) was administered by continuous pulsatile subcutaneous (s.c.) infusion via a portable pump. The effectiveness of pulsatile hMG treatment was first demonstrated in a control group comprising 7 females with regular ovulatory cycles, who underwent gonadotropin ovarian superovulation and subsequent IVF/GIFT procedures for tubal or male factor. All pulsatile s.c. hMG cycles were ovulatory and one clinical pregnancy was achieved. In this group, ovarian response was similar following intramuscular (i.m.) and pulsatile s.c. hMG therapy, with a marked reduction of preovulatory serum levels of oestradiol in the pulsatile s.c. hMG cycles. In a prospective study, 11 patients with overt polycystic ovary syndrome (PCO) who failed to ovulate in response to clomiphene, received i.m. hMG ovarian superovulation treatment in 19 cycles and pulsatile s.c. hMG in 21 cycles. Following i.m. hMG treatment, only 10 cycles were ovulatory; 7 cycles had to be cancelled for impending ovarian hyperstimulation syndrome. Following pulsatile s.c. hMG treatment, 15 cycles were ovulatory, only 3 treatment cycles had to be disrupted for multifollicular ovarian response. Both modes of treatment were similar in terms of requirement of hMG ampoules, number of preovulatory follicles, preovulatory serum levels of oestradiol and duration of the preovulatory oestradiol rise. The total duration of hMG treatment was significantly increased following pulsatile s.c. hMG. It is concluded, that in overt PCO syndrome, continuous pulsatile s.c. administration of hMG is an effective method to induce follicular maturation and to achieve ovulations.(ABSTRACT TRUNCATED AT 250 WORDS)