Hormonal alterations and pregnancy rates were compared between the clomiphene citrate (CC)-hMG combination cycle and the hMG cycle alone in an in vitro fertilization and embryo transfer program. In the CC-hMG cycle, the numbers of follicles developed, Oocytes recovered and embryos transferred were higher than those in the hMG cycle (p < 0.0l, p < 0.0l and p < 0.05, respectively). Pregnancy rates of the CC-hMG cycle (6.7%/operation, 7.1%/embryo transfer), however, were lower than those of the hMG cycle (25%/operation, 31.6%/embryo transfer). PRL levels in the hMG cycle increased according to estradiol levels. In the CC-hMG cycle, CC might inhibit estradiol-induced hyperprolactinemia and the increase was lower even if the estradiol level was much higher than that of the hMG cycle until day 2. On day 4, the PRL level in the CC-hMG cycle further increased. The thickness of endometrium on day -2 in the hMG cycle alone was much thicker than that in the CC-hMG cycle (9.8 ± 0.4 vs. 6.8 ± 0.4 mm, means ± SEM).