Abstract: We appreciate the comments of Drs. Aboulghar, Mansour, and Serour regarding our report of higher fertilization rate in sibling oocytes after ICSI compared with IVF in couples with unexplained infertility but not in couples with borderline semen parameters. With respect to the differences in results between our study and those of a larger multicenter trial (1Bhattacharya S. Hamilton M.P.R. Shaaban M. Khalaf Y. Seddler M. Ghobara T. et al.Conventional in-vitro fertilisation versus intracytoplasmic sperm injection for the treatment of non-male-factor infertility a randomized controlled trial.Lancet. 2001; 357: 2075-2079Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar), major differences in design could be the cause. We compared IVF and ICSI fertilization rates in sibling oocytes from a single retrieval (ICSI-IVF split). Bhattacharya et al. (1Bhattacharya S. Hamilton M.P.R. Shaaban M. Khalaf Y. Seddler M. Ghobara T. et al.Conventional in-vitro fertilisation versus intracytoplasmic sperm injection for the treatment of non-male-factor infertility a randomized controlled trial.Lancet. 2001; 357: 2075-2079Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar) randomized cases to either all IVF or all ICSI. This design allowed them to use implantation and pregnancy rate as main outcome measures. In the situation of borderline semen, differences in the very few studies in this subgroup of non-male-factor patients for whom ICSI was applied probably stem from inconsistencies in defining that parameter. We believe that because some cases of male infertility are undiagnosed before the initation of an IVF cycle, use of ICSI provides us with a powerful tool to further understand the capacity of sperm to fertilize oocytes while rescuing some cases from fertilization failure. However, we do recommend that the decision to perform ICSI be made judiciously.