Scientists in the United States have complained to a Senate subcommittee that because of 'severe restrictions' placed on human embryonic stem cell (ES cell)  research by President Bush, the science is moving 'exceedingly slowly' in America.

On 9 August last year, President Bush limited the availability of federal funds for ES cell research to studies conducted on stem cells derived and isolated before that date. According to the National Institutes for Health (NIH), there are 78 ES cell lines available worldwide to be used by federally-funded US researchers.

Despite this, American scientists claim that access to the ES cell lines is problematic, mainly because of financial reasons and restrictions placed on their export and use by some other countries where they are held. Dr George Daley, of the Whitehead Institute in Boston, Massachusetts, said that 'perhaps only a handful' of cell lines were actually available to scientists. Dr Curt Civin, from Johns Hopkins University School of Medicine, said that the cell lines were accessible 'only to those persistent and patient enough to jump through a series of hoops and endure lengthy waits.'

Both scientists advised the Senate subcommittee that the NIH should establish a central storage and distribution facility. Dr Gerald Schatten, of Pittsburgh University, said that the federal government needed to give ES cell research 'enthusiastic support' or the work 'would proceed so slowly that the public would grow frustrated and taxpayer support would dry up.'

Responding to the criticisms, Senator Arlen Specter, co-sponsor of an earlier bill, pledged to continue his efforts to get legislation passed through Congress that will allow more funding of ES stem cell research in the US.