In experiments with mice, two separate groups of scientists have found ways to derive embryonic stem cells without destroying viable embryos. If these techniques can be replicated in humans, they may help ease ethical and political concerns over stem-cell use. "The hope is that these will be a platform for human studies in the future," said George Daley, a stem-cell researcher at Harvard Medical School in Boston, who wasn't involved in either of the studies. Dr. Daley cautioned that the experiments "raise more questions than they answer."