Intracytoplasmic sperm injection (ICSI) was successful in the mouse when a piezo-driven micropipette was used instead of a mechanically driven conventional pipette. Eighty percent of sperm-injected oocytes survived, and approximately 70% of them developed into blastocysts in vitro. When 106 embryos at the 2- to 4-cell stage were transferred to eight naturally mated foster mothers, 30% of the embryos (25-43%, depending on the host) reached the full term. Except for two that were cannibalized soon after birth, all of the young (30 pups) grew into normal adults. Studies of this type on the mouse may increase understanding of the fertilization process and of how ICSI works.