This article reports on the effects of human chorionic gonadotropin (hCG) on progesterone (P) and estradiol (E2), luteal phase length, and conception in 116 cycles treated by in vitro fertilization and embryo transfer (IVF-ET). In 60 cycles, the luteal phase was supported by hCG, 1500 IU three times at 2-day intervals from the day of ET. The remaining 56 cycles served as controls. hCG significantly increased the P level (93 +/- 53 versus 62 +/- 46 ng/ml), the P/E2 ratio, and the luteal phase length (17.4 +/- 1.3 versus 12.2 +/- 1.7 days). However, the total pregnancy rate did not significantly differ between the two groups, though the pregnancy rate after transfer of two or three embryos was slightly higher in the hCG group (26.9 versus 22% in the control group), as was the rate of implanted embryo per transferred embryo after transfer of two or three embryos (25 versus 15.3%). It was concluded that, while hCG increased the magnitude and duration of the luteal P secretion, it did not clearly improve the pregnancy rate.