Microsurgical enucleation of a single pronucleus from each of three tripronuclear zygotes was performed and the embryos were transferred to a 38-year-old woman on day 3 after fertilization. A normal healthy baby boy was born at 38 weeks and 4 days gestation, demonstrating that with polyspermic fertilization, removal of the extra male pronucleus allows the zygote to develop normally.