The luteal phase hormone profiles of two groups participating in the Yale in vitro fertilization (IVF) program were compared. A control group (group I) consisted of 28 women (28 cycles) who received our standard ovulation induction regimen (no luteal phase support). The treatment group (group II) consisted of 40 women (42 cycles) who were prospectively studied after receiving luteal phase support with 10,000 IU human chorionic gonadotropin (hCG) 5 days after the initial hCG dose. The groups were matched for age and cause of infertility. Estradiol (E2) and progesterone (P) were measured on the day of embryo transfer and every 3 to 4 days thereafter. Luteal phase hCG support significantly augmented (1) E2 and P levels in the conception cycles of group II compared with group I and (2) P levels in the nonconception cycles of group II compared with group I. The midluteal decline in E2 and P that was observed in group I was minimized or prevented in group II. An ongoing pregnancy rate of 19% was achieved in group II. This was not statistically different from the 13% ongoing pregnancy rate noted in a separate group of 163 tubal factor couples undergoing IVF after our standard ovulation induction regimen during the period of the study. In summary, the luteal phase hormone profiles of IVF cycles were improved by supplementation with hCG. It is concluded that this type of intervention may serve to rescue potentially failing corpora lutea and thereby optimize the peri-implantation hormonal milieu.