The history of in vitro fertilization (IVF) and embryo transfer (ET) goes back to the early 1890s when Walter Heape, a professor and physician at the University of Cambridge, England, reported the first known case of embryo transplantation in rabbits, long before the applications to human fertility were even suggested. In 1934 Pincus and Enzmann, from the Laboratory of General Physiology at Harvard University, published a paper in the Proceedings of the National Academy of Sciences of the USA, raising the possibility that mammalian oocytes can undergo normal development in vitro. Two decades later, in 1948, Miriam Menken and John Rock retrieved more than 800 oocytes from women during operations for various conditions. One hundred thirty-eight of these oocytes were exposed to spermatozoa in vitro, and they published their experiences in the American Journal of Obstetrics and Gynecology.