OBJECTIVE: To investigate the effects of adrenal suppression with dexamethasone (DEX) on P and androgen profiles during controlled ovarian hyperstimulation (COH) for IVF-ET. DESIGN: Prospective controlled trial. SETTING: In vitro fertilization program, Clamart, France. PATIENT(S): One hundred twenty IVF-ET candidates aged 25 to 39 years undergoing 120 COH cycles. INTERVENTION(S): Group A: 60 women received a time-release GnRH agonist (GnRH-a) on cycle day 2. After pituitary desensitization was confirmed, 1 mg/d DEX was administered daily until hCG. Ovarian stimulation with hMG was started on the 7th day of DEX. Group B: 60 other women received an identical treatment except DEX was omitted. MAIN OUTCOME MEASURE(S): Plasma E2, P, androstenedione (A), and T were measured 18 days after GnRH-a, on the 7th day of DEX in group A, and on the day of hCG. RESULT(S): Peak plasma E2 levels were similar in groups A and B. After GnRH-a, P and androgen levels were low in both groups. In group A, an additional decrease in these hormones was observed after 7 days of DEX. During COH, we observed similar absolute increases of P, A, and T in groups A (+0.52, +1.56, and +0.12 ng/mL, respectively) and B (+0.55, +1.66, and +0.17 ng/mL, respectively). CONCLUSION(S): As expected, DEX lowered additionally P, A, and T levels from values achieved after GnRH-a alone, reflecting the adrenal contribution to the circulating levels of these hormones at baseline. Yet, the net increases in P, A, and T seen in COH were unaltered by DEX treatment, indicating that this phenomenon results solely from an effect of exogenous gonadotropins on the ovary.