WASHINGTON—President Bush this week vetoed legislation that would have lifted limits on federally funded research on embryonic stem cells. Angry congressional advocates immediately pledged to override the veto (although they acknowledge they are still shy of the two thirds majority needed) and took new steps to free up federal monies for such research, which holds the promise of new treatments for debilitating diseases from Parkinson's to diabetes.

Just a day after the president nixed the measure, the Democratic-controlled Senate Appropriations Committee added a provision to a money bill that would allow taxpayer dollars to be spent on stem cells extracted from embryos before June 15. That expands a ban Bush imposed six years ago, limiting federal research to about 20 cell lines derived from embryos before August 2001, many of which scientists say have been compromised or corrupted.

"Once again, the president has ignored the will of the American people, of leading medical researchers and of a bipartisan majority of the Congress," House Speaker Nancy Pelosi (D–Calif.) said in a statement released after the veto. "His cruel veto says 'no' to the hopes of millions of families across America."

The move marked the second time in two years that Bush, bowing to his conservative base, vetoed such a package, despite growing public support and a new study showing that most patients at U.S. fertility clinics would likely donate surplus stored embryos for stem cell research if given the option.

"If this legislation became law, it would compel American taxpayers for the first time in our history to support the deliberate destruction of human embryos," Bush said. "I will not allow our nation to cross this moral line."

He also signed an executive order urging scientists to work with the federal government to come up with ways to derive cells without destroying embryos.

But backers point out that the bill would only permit federally funded scientists to use embryos left over from fertility clinics that patients choose to donate and that otherwise would be discarded. The legislation would also set up strict ethical guidelines to govern research.

The veto came the same day that Duke University in Durham, N.C., and Johns Hopkins University in Baltimore released a report showing that the majority of people with frozen embryos stored at U.S. fertility clinics would likely donate them to create stem cell batches or lines for research.

Researchers sent surveys to more than 2,200 patients at fertility centers in California, Colorado, Maryland, Missouri, New Jersey, North Carolina, Oregon, Pennsylvania and Washington, D.C.

They report in today's issue of Science that 60 percent of the 1,200 patients who responded said they would donate surplus embryos for use in stem cell research; only 22 percent said they would hand over unused embryos to other infertile couples—the option favored by Bush and other embryonic stem cell research detractors.

"Until now, the debate about federal funding for embryonic stem cell research has been dominated by lawmakers and advocates. But what about the preferences of infertility patients, who are ethically responsible for, and have legal authority over, these embryos," said study co-author Ruth Faden, director of Johns Hopkins's Berman Institute of Bioethics. "These patients face the often morally difficult task of deciding what to do with their remaining cryopreserved embryos. In the end, it is these people who determine whether embryos are available for adoption or for medical research.''

Co-author Anne Drapkin Lyerly, a Duke bioethicist and professor of obstetrics and gynecology, said the findings could have "significant implications" on policy and research efforts.

"Previous research indicates that there are approximately 400,000 frozen embryos stored in the United States; if half of those belong to people who are willing to donate embryos for research," she said, "and only half that number were in fact donated, there could still be 100,000 embryos available for research."