At 9:00 in the evening on January 29, just as President George W. Bush was about to begin his first State of the Union address, I gathered with three anxious scientists in a small, windowless laboratory in Worcester, Massachusetts. We were at Advanced Cell Technology—a privately owned biotechnology company that briefly made international headlines last fall by publishing the first scientific account of cloned human embryos. The significance of the achievement was debatable: the company"s most successful embryo had reached only six cells before it stopped dividing (one other had reached four cells, another had reached two)—a fact that led to a widespread dismissal, in the media and the scientific community, of ACT"s "breakthrough". The work was largely judged to be preliminary, inconsequential, and certainly not worthy of headlines. Many people in political and religious circles, however, had a decidedly different view. They deemed ACT"s work an ethical transgression of the highest order and professed shock, indignation, and horror.Nonetheless, ACT was pressing ahead—which was why I had come to the company"s cloning lab that night in January. The door to the lab was locked; a surveillance camera mounted on the ceiling watched our every move; and the mood was at once urgent and tense. A human egg, retrieved just hours earlier from a young donor, was positioned under a microscope, its image glowing on a nearby video monitor. The egg"s chromosomes would shortly be removed, and the scientists in the room would attempt to fuse what remained of the egg with a human skin cell. If the procedure succeeded, the result would be a cloned human embryo.Skin cell to embryo—it"s one of the most remarkable quick-change scenarios modern biology has to offer. It"s also one of the most controversial. Since the announcement, in 1997, of the cloning of the sheep Dolly, attempts to use human cells for cloning have provoked heated debate in the United States, separating those who have faith in the promise of the new technology from those who envision its dark side and unintended consequences.Crucial to the debate is the fact that human cloning research falls into two distinct categories: reproductive cloning, a widely frowned-on effort that aims to produce a fully formed child; and therapeutic cloning, a scientifically reputable procedure that takes place entirely at the microscopic level and is designed to advance medical therapies and cure human ailments. The two start out the same way—with a new embryo in a Petri dish. But the scientists I was observing in the lab had no intention of creating a person. Instead they were embarking on an experiment that, if successful, would be a first step toward creating radical new cures for patients like the donor of the skin cell—Trevor Ross (not his real name), a two-year-old boy afflicted with a rare and devastating genetic disease.The mood in the lab was tense in part because of the uncertain outcome of the experiment. But it was also tense because of concern over what President Bush might say about cloning in his address to the nation. A radio in one corner of the room was tuned to the broadcast as the scientists began their work, and they were listening carefully: in perhaps no other fields of science are researchers as mindful of which way the political winds are blowing. The ACT scientists had good reason to be concerned—what they were doing that night might soon be made illegal.