In 105 patients with the past history of poor response to the previous controlled ovarian hyperstimulation(COH) due to poor follicular growth or premature LH surge, the effectiveness of pituitary suppression with gonadotropin-releasing hormone agonist(GnRH agonist) in IVF/GIFT program was evaluated in 112 cycles of COH using a combination regimen of Leuprolide acetate (Lupron TAP Pharmaceuticals, USA) and FSH/hMG or pure FSH from May to December, 1989 at SNUH. Starting on day 21 of the menstrual cycle(MCD #21, Day 1), Lupron (1.0mg/day, subcutaneous) was administered once a day till next MCD #3(suppression phase). After the confirmation of pituitary suppression, ovarian follicular growth was stimulated with FSH/hMG or pure FSH from MCD #3(Day + 1), and Lupron was continued with hMG or FSH until hCG administration (D 0) (stimulation phase). After suppression phase, serum E2 level decreased from 183.7${pm}$95.1(Day 1) to 17.4${pm}$12.3pg/ml (Day +1), and serum progesterone level from 19.17${pm}$8.67 to 0.12${pm}$0.05ng/ml. But there was no decresas in serum LH and FSH levels; LH from 12.74${pm}$6.21 to 15.49${pm}$4.93mIU/ml,FSH from 7.60${pm}$3.84 to 8.58${pm}$3.15 rnlU/ml. There was no occurrence of premature LH surge during COH. Eleven cycles(9.8%) were cancelled due to poor follicular growth during stimulation phase, and 3 cycles (3.0%) failed in the transvaginal oocytes fretrieval. Serum E2 level was 1366.8${pm}$642.4 on D 0 and 1492.3${pm}$906.9pg/ml on D+1. 7.00${pm}$3.32 follicles(FD${geq}$12mm) were observed on D 0, and 6.11${pm}$4.15 oocytes were retrieved, with the oocyte retrieval rate per follicle of 95.0%. 3.59${pm}$2.57 oocytes were fertilized and cleaved with the oocyte cleavage rate of 55.7%. In 83 IVF patients, 4.08${pm}$2.39 embryos were transferred, and 16 pregnancies were obtained with the pregnancy rate per ET 2.39 mebryos were transferred, and 16 pregnancies were obtained with the pregnancy rate per ET of 19.3%. In 6 GIFT patients, 7.83${pm}$3.31 oocytes were retrieved and transferred with maximum number of 6, but no pregnancy was obtained. When compared with the previous 108 cycles of COH using FSH/hMG or pure FSH regimen, the cancellation rate during COH was significantly decreased, and all the parameters of the outcome of COH including the pregnancy rate were increased. These data suggest that GnRH agonist therapy for pituitary suppression is an effective adjunct to the current gonadotropin regimens for COH in IVF/GIFT and can increase the probability of oocytes retrieval and pregnancy, especially in the previous poor responders.