Administration of human chorionic gonadotropin (hCG) to promote ovarian steroid secretion near the time of recognition of pregnancy was evaluated. Neither 500 or 1000 IU of hCG caused a significant increase in luteal function as determined by progesterone (P(4)) concentrations in peripheral blood following treatment on Day 12. Estradiol concentrations were elevated (P<0.01) for the 500 IU hCG group on Days 13, 14, 15 and 16 versus the control group. The 1000 IU of hCG group had three-to five-fold greater (P<0.01) estradiol concentrations than controls on Days 14, 15 and 16 post mating. Treatment with hCG also reduced (P<0.05) the number of resorbed embryos. The results suggest that hCG treatment on Day 12 of pregnancy reduced embryo loss and influenced peripheral estradiol secretion patterns.