The leading scientist in the Bush administration has broken with his boss over embryonic stem cell research. "From my standpoint, it is clear today that American science will be better served, and the nation will be better served, if we let our scientists have access to more stem cell lines," Dr Elias A. Zerhouni, director of the National Institutes of Health, told a Senate committee.

"We cannot, I would think, be second-best in this area," Zerhouni said. "I think it is important for us not to fight with one hand tied behind our back here, and NIH is key to that."

Studies claiming that adult stem cells have as much potential as embryonic stem cells "do not hold scientific water," Zerhouni claimed. "I think they are overstated. We do not know at this point where the breakthrough will come from? All angles in stem cell research should be pursued."