Advanced Cell Technologies (ACT) has reported the successful cloning of a human embryo by removing DNA from the skin of a man's leg and inserting it into a cow's egg, which previously had its nucleus removed. The announced cloning took place in November 1998, although ACT may have performed the same experiment years before. Researchers allowed the cloned embryo to develop for 12 days before halting the experiment. Several more clonings have reportedly been done with the goal of harvesting stem cells from embryos. Stem cells are found inside embryos during the first two weeks of their development and have the potential to develop into any kind of cell in the human body. After two weeks stem cells differentiate into more specialized tissues.

Tissues created from stem cells could be used to treat nerve damage, Parkinson's disease, and diabetes. Stem cells could also be used to create organs for transplantation. In addition many other medical benefits are expected. See the essay, "The Benefits of Human Cloning."

ACT's clone may be the first cloned human embryo. There were reports of similar work in South Korea, but it remains unclear as to whether those scientists were successful.