In vitro fertilization-embryo transfer seems to be an effective treatment for unexplained infertility. Some IVF centers always perform intracytoplasmic sperm injection in these circumstances being concerned that fertilization failure may occur by conven­tional oocyte insemination. However, other IVF centers perform intracytoplasmic sperm injection on half of the oocytes and do con­ventional insemination on the other half. However, if the group with conventional oocyte insemination had a good fertilization rate, in the future intracytoplasmic sperm injection would not be performed. Other lVF centers would inseminate all the oocytes with conventional insemination and not consider intracytoplasmic sperm injection in the future unless there were poor fertilization rates. The aforementioned studies suggest that prior to considering conventional insemination that as a minimum the simple inexpensive hypo-osmotic swelling test be performed and strong consideration also be given to the sperm stress test and SCSA. Similarly, even though IUI is less risky and costly than IVF-ET, there still is a moderate expense and risk involved, especially when superovulation is used. Thus, consideration for performing these tests should also be given even prior to IUI. This is especially important for subnormal HOST scores where pretreatment of the sperm with the protein digestive enzyme chymotrypsin when preparing the sperm has been demonstrated to markedly improve pregnancy rates.