The access to human pre‐implantation embryos that is afforded by procedures now developed for the treatment of infertility presents the possibility of very early prenatal diagnosis, before implantation in the uterus, of certain genetic diseases. Only the normal embryos would be replaced in the mother for initiation of implantation and pregnancy. Early experiments on a mouse model for Lesch‐Nyhan syndrome (HPRT‐deficiency) show that pre‐implantation diagnosis of genetic disease is feasible.