To compare the effectiveness of IM P and IM P plus oral phytoestrogens for lut eal phase support in patients undergoing IVF-ET cycles. Prospective, controlled , randomized trial. University Hospital, Perugia, Italy. Two hundred thirteen in fertile patients undergoing IVF-ET were included in the study. The inclusion cr iteria were use of a GnRH agonist for pituitary down-regulation and age < 40 ye ars. The total number of cycles performed was 274. Patients were assigned to rec eive either IM P (50 mg daily) plus placebo or P (50 mg daily) plus phytoestroge n supplementation (1,500 mg daily) for luteal phase support starting from the ev ening of oocyte retrieval until either a serum pregnancy test result was negativ e or embryonic heartbeat was sonographically confirmed. The outcomes of IVF-ET were evaluated in both study groups in terms of implantation rate, biochemical p regnancy rate (PR), clinical PR, spontaneous abortion rate, and ongoing pregnanc y/delivered rate. Statistically significant higher values for implantation rate, clinical PR, and ongoing pregnancy/delivered rate were recorded in the patients who received P plus phytoestrogens for luteal phase support in comparison with patients receiving P and placebo. Although the results of this study encourage t he use of phytoestrogens for luteal phase support in patients undergoing IVF-ET program, more studies are necessary to support the hypothesis that phytoestroge ns have a beneficial effect in IVF cycles. University of Perugia, Italy. Two hundred thirteen in fertile patients undergoing IVF-ET cycles The inclusion cr iteria were use of a GnRH agonist for pituitary down-regulation and age <40 ye ars. The total number of cycles performed was 274. Patients were assigned to rec eive either IM P (50 mg daily ) plus placebo or P (50 mg daily) plus phytoestroge n supplementation (1,500 mg daily) for luteal phase support starting from the ev ening of oocyte retrieval until either a serum pregnancy test result was negativ e or embryonic heartbeat was sonographically confirmed. The results of IVF-ET were evaluated in both study groups in terms of implantation rate, biochemical p regnancy rate (PR), clinical PR, spontaneous abortion rate, and ongoing pregnanc y / delivered rate. Statistically sig nificant higher values ​​for implantation rate, clinical PR, and ongoing pregnancy / delivered rate were recorded in the patients who received P plus phytoestrogens for luteal phase support in comparison with patients receiving P and placebo. Although the results of this study encourage he use of phytoestrogens for luteal phase support in patients undergoing IVF-ET program, more studies are necessary to support the hypothesis that phytoestroge ns have a beneficial effect in IVF cycles.