Washington

Top officials at the US National Institutes of Health (NIH) have made a pitch for the country's lawmakers to loosen rules that govern federal funding for human embryonic stem-cell research.

The officials lobbied senators who control the agency's budget at a hearing on 6 April. The current policy, set out by President George Bush, prevents scientists from using federal funds to do research on human embryonic stem-cell lines derived after 9 August 2001.

“Access to more cells is seen by scientists as very important to their progress,” NIH director Elias Zerhouni told the hearing.

In written testimony, other NIH leaders were more forceful. “The state of the science is evolving very rapidly and limitations of the president's policy are becoming more apparent,” wrote James Battey, director of the National Institute on Deafness and Other Communication Disorders and former head of the NIH Stem Cell Task Force.

Zerhouni has said in the past that scientists should exhaust all the work they can possibly do on permitted stem-cell lines before revisiting the Bush policy. He has also pointed out that the policy is based not only on science, but on ethics and morality. At the hearing he was careful to state that he did not advocate overturning the policy.

But momentum has been building in Congress to do just that. Scientists have complained loudly that too few lines are available, and that they are contaminated by mouse cells. Support has been growing in the Senate to overturn the Bush rules, and leaders in the House of Representatives last month indicated that they may also be open to revisiting the policy (see Nature 434, 548; 2005 10.1038/434548a).