A number of recent papers have described the successful derivation of egg and sperm precursor cells from mouse embryonic stem cells—so-called “artificial” gametes. Although many scientific questions remain, this research suggests numerous new possibilities for stem cell research and assisted reproductive technology, if a similar breakthrough is achieved with human embryonic stem cells. The novel opportunities raised by artificial gametes also prompt new ethical questions, such as whether same-sex couples should be able to access this technology to have children who (...) are genetically related to them both.THE CREATION OF “ARTIFICIAL” GAMETESOver the past two years, a number of papers have been published detailing the first successful attempts at differentiating mouse embryonic stem cells into egg1 and sperm2 precursor cells. Previously, researchers had used embryonic stem cells to generate tissues such as brain, liver, and pancreatic cells, but not germ cells of any kind. Production of gamete precursor cells was achieved initially through allowing stem cell lines to differentiate more or less randomly, but recent research has focused on identifying the precise ways in which differentiation into gametes can be precipitated and controlled. These breakthroughs make it seem likely that ongoing research on human stem cells will yield similar possibilities,3 raising questions over the practicalities of what might be achieved with such “artificial” gametes. In turn, the novel opportunities presented by artificial gametes raise a number of ethical concerns.The initial breakthrough, namely the obtaining of egg cells from mouse stem cells, was achieved by means of relatively simple science. Rather than coaxing stem cells to develop into eggs using complicated cocktails of growth factors, researchers adopted standard cell culture conditions, but grew the cells at higher density than usual.3–6 Growing the cells in this way led to the formation of ovary-like cell aggregates, which (when separated and stimulated with …. (shrink)