Genetically modified mice contribute greatly to a better understanding of molecular mechanism underlying normal physiology and disease. Transgenic Core Facility generates transgenic mice by microinjection of foreign DNA into pronucleus of one-day embryo, performs rederivation of mouse lines and cryopreservation of mouse embryos. This year we have produced 7 new transgenic lines, rederived 20 lines and cryopreserved 16 mouse lines. We have also set up several new procedures, including reconstitution of mouse lines from frozen embryos, sperm collection and freezing, in vitro fertilization for rescue and rapid expansion of mouse colonies, and cryopreservation of embryos following in vitro fertilization.