Twenty patients were given norethindrone acetate (NET) to program the initiation of controlled ovarian hyperstimulation and to coordinate follicular aspiration with surgery to obtain spermatozoa from the husband. Patients received NET, 10 mg/day orally, starting between days 2 and 4 of the cycle. The duration of NET therapy varied from 9 to 37 days. The mean time of onset of vaginal bleeding, after cessation of NET, was 2.9 +/- 0.7 days. Ovarian stimulation was carried out with a combination of a luteinizing hormone releasing hormone analog, follicle-stimulating hormone and human menopausal gonadotrophin. The day of human chorionic gonadotrophin (HCG) administration ranged from day 8 to day 15 of the cycle (10.1 +/- 1.7). On the day of HCG injection, the mean E2 level was 2188 +/- 1126. The mean number of follicles aspirated was 18.4 +/- 9.9 per cycle. The mean number of oocytes collected per cycle was 15.5 +/- 8.5. There was no correlation between duration of NET suppression and the number of days of gonadotrophin therapy needed to reach HCG administration. The large number of oocytes retrieved is probably related more with the fact that the patients represented a group with a purely male factor of infertility, than by the specific drug protocol utilized. Our results demonstrate that the ovarian response to gonadotrophin stimulation was not affected by NET administration. The main advantages of the use of this drug for cycle control are that its administration is oral, simple and inexpensive.