OBJECTIVE: To investigate the effects of hCG administered to patients undergoing controlled ovarian hyperstimulation on levels of ovarian hormones, including androgens. DESIGN: Prospective analysis. SETTING: Assisted Reproduction Unit, Hopital Antoine Beclere, Clamart, France. PATIENT(S): Six infertile, normally ovulating volunteers. INTERVENTION(S): The women underwent controlled ovarian hyperstimulation with a GnRH agonist and hMG for IVF-ET. After the i.m. administration of hCG (10,000 IU), blood samples were drawn every 6 hours for 4 days. MAIN OUTCOME MEASURE(S): Plasma androstenedione, testosterone, progesterone, and E2 profiles. RESULT(S): Treatment with hMG increased plasma androstenedione and testosterone levels 1.4-fold and 2.6-fold, respectively. The administration of hCG did not increase plasma androstenedione and testosterone levels any further; mean daily levels remained at 2.3 ng/mL and 0.64 ng/mL, respectively. Circadian changes in androstenedione levels were evident after hCG administration. Plasma progesterone levels neared 10 ng/mL 19 hours after hCG administration, plateaued for 24 hours, and increased again thereafter. Plasma E2 levels declined during the first 2 days after hCG administration and then increased, concomitant with the second phase of progesterone elevation. CONCLUSION(S): In patients undergoing controlled ovarian hyperstimulation, androgen levels increased in response to hMG treatment, but no further elevation occurred after hCG administration. The rate of elevation of progesterone levels and the absolute levels achieved were 3-fold and 10-fold higher, respectively, than those observed during spontaneous menstrual cycles.