The revised guidelines for funding human embryonic stem-cell research published by the US National Institutes of Health last week provide an imperfect solution to an insoluble problem. The research potential of the cells demands that NIH-funded biomedical researchers should be allowed to use them. Embryonic stem cells can divide for ever and, with work, could be steered into becoming virtually any other cell type. Harnessing stem cells could one day provide treatments for spinal cord injury, neurodegenerative diseases and diabetes. But many in the United States do not believe this outweighs the moral price of deriving research materials from discarded human embryos.

The guidelines allow federal funds for stem-cell research but not for the derivation of the cells themselves. They satisfy US researchers' immediate concerns, but they rest on fragile logic. Researchers who receive federal funds to study the cells will end up using federal grant money to pay those who derive the cells anyway. Opponents of abortion correctly point out that the rules do not clarify existing laws against embryonic research, but rather circumvent them. They say funding experimentation tacitly supports derivation, and the destruction of embryos which that entails.

Researchers on federal grants worry that privately funded colleagues will gain an edge in experimental manipulation of stem cells which they derive for themselves. NIH-funded researchers will be limited to the cell lines provided by private firms, rather than being free to create and tailor lines to meet their own needs. Scientists in Britain and elsewhere will probably gain permission to both derive and experiment on embryonic stem cells (see Nature 406, 815; 2000).

Reliance on the distinction between use and derivation leaves the future of the research uncertain, subject to the influence of politics and of the courts. If vice-president Al Gore wins the US presidential election, he will be inclined to let it continue under the NIH guidelines. But if George W. Bush prevails, he could easily pass an executive order banning all federally funded stem-cell research.

A bill proposed by Senator Arlen Specter (Republican, Pennsylvania) to allow funding for use and derivation of embryonic stem cells would end the ambiguity. But the bill hasn't yet been brought to a vote in the Senate and will struggle to muster support in the House of Representatives. Progress must await the outcome of the presidential and Congressional elections in November.