Fifty patients (normal responders) received either human menopausal gonadotropin (hMG) alone (control group) or leuprolide + hMG (leuprolide group). The use of leuprolide was associated with a reduction of hMG requirements (14.8 versus 17.8 ampules, P = 0.02) and the abolition of spontaneous luteinizing hormone surges (nil versus 3, P = 0.006). The rate of fertilization (87% versus 65%, P = 0.003) was higher in the leuprolide group. Pituitary and ovarian suppression was effected for 16 subjects who had previously shown a poor follicular response and a further 19 subjects who had previously responded abnormally. The poor responders required more hMG (43.9 versus 27.1 ampules, P less than 0.001), achieved a lower estradiol maximum (5.1 versus 12.1 nmol/l, P less than 0.001), and had fewer oocytes recovered (4.1 versus 11.5, P less than 0.001), than the abnormal responders.