At infertility clinic, department of Obstetrics and Gynegology, Kyung Hee Medical Hospital, 80 patients who underwent IVF-ET from January to July, 1989 were evaluated for the prediction of endogenous LH Surge and its effects on outcome of controlled ovarian hyperstimulation (COH) were compared among LH Surge group without hCG given (N=18), with hCG given (N=5), and no-LH Surge group with hCG given (N=57). LH Surge were occurred in 23(28.7%) out of 80 patients studied. Serum E2 levels on Day-1, Day 0, Day+1, were no significant different among three groups. When basal serum LH/FSH ratio is above 1.0, the possibility of endogenous LH Surge is much higher (56.3% in LH Surge group without hCG given). Serum P4 levels on Day 0 were significantly increased in LH Surge group without hCG given. Cycles which serum P4 level is higher than l.0ng/ml were 70.6% of LH Surge group without hCG given. But there was no significant interrelationship between endogenous LH Surge and serum P4 rising rate as an efficient predictor of the occurrence of endogenous LH Surge in COH for IVF. There was no significant differences in number of follicles, follicular size on Day-1, Day 0, Day+1, and number of oocyte collected per cycle. The oocyte fertilization rate of No-LH surge group with hCG given was significantly higher than LH Surge group without hCG given. There was no significant difference in oocyte cleavage rate among three groups.