An emotional vote last week in the House of Representatives to expand federal funding for stem cell research was the latest spasm in a dispute that has been raging since 1998, when American researchers first cultured these seemingly miraculous cells from a human embryo.

Stem cells are controversial worldwide but the intensity of the US debate is unmatched. On one side stands the power of American bioscience, which believes it has a mission to lead the world to a healthier future - and feels thwarted by the restrictions imposed by President George W. Bush in 2001. Embryonic stem cells are a promising route to a new era of "regenerative medicine" because they can develop into any tissue, from brain to bone, and they therefore offer hope of treating diseases ranging from diabetes to Parkinson's.