OBJECTIVE: To determine the predictive value of preovulatory serum concentrations of P, E2, and LH for pregnancy achieved with IUI after superovulation with and without adjunctive leuprolide acetate (LA) therapy. DESIGN: Randomized, crossover study of superovulation with and without LA therapy. SETTING: Infertility clinic. PATIENTS: Subfertile patients referred for superovulation and IUI. MAIN OUTCOME MEASURES: Preovulatory serum concentrations of P, E2, and LH on the day of hCG administration; pregnancy. RESULTS: Preovulatory serum concentrations of P, E2, and LH had equivalent predictive value for pregnancy during cycles stimulated without LA therapy. No single parameter was particularly useful in clinical decision making. Threshold P concentrations proposed in other studies as useful in predicting pregnancy did not correlate with cycle fecundity. The predictive value of preovulatory concentrations of P during superovulation with adjunctive LA therapy was significantly worse than P concentrations during superovulation without LA therapy. CONCLUSIONS: Preovulatory serum P, E2, and LH concentrations in superovulation and IUI are not helpful in determining prognosis for pregnancy. The relative utility of predictive parameters may vary for different treatment regimens.