&NA;Ovarian follicular growth was stimulated in 4 patients with clomiphene resistant polycystic ovary (PCO)‐like disease, with “pure” human pituitary FSH during 10 cycles. In 8 cycles additional hCG was given to induce ovulation. Serum LH and FSH and plasma estradiol and progesterone were determined daily. From the response patterns of steroidogenesis, four functional stages of follicular development can be distinguished, each subsequent stage being characterized by an increasing spontaneous estradiol production and a decreasing capacity to produce extra estradiol in response to stimulation with additional hCG. It is concluded that the unpredictable response to gonadotropin stimulation of patients with PCO‐like disease is due to the varying state of development of the follicles at the start of the stimulation. The suggestion is made, based on the different responses in 3 cycles of the same patient (EW), that the lack of positive estrogen feedback in patients with PCO‐like disease may be a hyposensitivity to estrogens rather than an absolute insensitivity.