Ovarian stimulation and corpus luteum function in human in vitro fertilization and embryo transfer were investigated. Thirty-three cycles were treated with clomiphene citrate (CC) alone and 56 cycles with a CC/human menopausal gonadotropin (hMG) combination, and the latter was divided into three groups in the luteal phase; untreated (CC/hMG-NO) (n = 21), treated with progesterone (CC/hMG-P) (n = 23), and treated with human chorionic gonadotropin (hCG) (CC/hMG-hCG) (n = 12). There were many more increases in the number of aspirated follicles, recovered oocytes, and transferred embryos in the CC/hMG group than in the CC group. A significant correlation was found between the numbers of aspirated follicles and serum estradiol (E2) peaks in the follicular phase, and also between serum E2 peaks in the follicular phase and serum progesterone (P) maximum levels in CC and CC/hMG-NO. No significant difference was observed in serum P levels in the midluteal phase among four groups, though their levels were given in the following order; CC/hMG-hCG greater than CC/hMG-P greater than CC/hMG-NO. P/E2 ratios for the luteal phase in the CC/hMG-hCG group were significantly higher than those of other groups, but the pregnancy rate for the CC/hMG-hCG group was the lowest in the four groups. In conclusion, the high P and high P/E2 ratios following luteal treatment were not necessarily connected with pregnancy.