Those difficult cases whereas due to an unknown origin of infertility or another cause, the spermatozoid is introduced directly in the oocyte. Only one spermatozoid is necessary for each oocyte. This technique has allowed that those males who were previously not candidates for reproduction, nowadays they are the real candidates to be natural fathers, so that we can even capture spermatozoids from epididimal aspirates or testes biopsy. After 16-20h to have spermatozoid and oocyte been in contact, wether by FIV or by ICSI, we observe if fecundation has taken place. During the next two days we evaluate if embryos are dividing up rightly, and three days after oocyte extraction, embryos are transferred to uterus. No anesthesia is required at this point. The maximum number of embryos to transfer according to Spanish legislation is three, to avoid multiple pregnancy.