Objective: To determine if pregnancy rates (PRs) for clomiphene citrate (CC)-stimulated IVF-ET can be increased by luteal support with E2 and P. Design: Prospective randomized crossover clinical study. Setting: Infertile women volunteers in an academic research environment. Patients: Ninety-three infertile women underwent a total of 143 IVF-ET cycles using CC for ovulation induction. Interventions: Each woman received either no luteal support (control group) or luteal support with both oral E2 (2 mg three times daily) starting on the day of retrieval and vaginal P suppositories (100 mg twice daily) starting on the day of ET. Main Outcome Measure: Clinical PR. Results: In 79 of 143 (55%) of the cycles, at least one embryo was transferred. Compared with the control group (n = 35 cycles), the luteal support group (n = 44 cycles) had a significantly higher PR per retrieval (control: 2% versus luteal support: 16%) and were older (control: 33 ± 4 versus luteal support: 35 ± 4 years; mean ± SEM). They did not differ in terms of E2 or P levels, endometrial thickness on the day of hCG, number of follicles > 16 mm in diameter, mature oocytes retrieved, or embryos transferred. Conclusions: Luteal support with both E2 and P significantly increases the clinical PRs for CC-stimulated IVF-ET.