The US Senate has voted to ease restrictions on using federal funds for stem-cell research, defying the threat of a veto by President George W Bush.
Opinion polls suggest most Americans back the research
The Democrat-controlled Senate passed the vote with a majority of 63 to 24 - just short of the two-thirds required to override a presidential veto.
Mr Bush has said he will use his powers to veto the Senate's vote. He vetoed a similar draft bill last year.
Democrats argue that the restrictions are impeding vital medical research.
Upon taking charge of Congress last year, the party vowed to push for easing curbs on federal funding for stem-cell research.
Stem cells are immature cells, created shortly after conception, which have the capacity to turn into any kind of tissue in the body.
Scientists hope to use stem cells taken from frozen human embryos to repair tissue affected by disease or injury.
Key sources for stem cells are adult organs or embryonic cells
Adult stem cells are identified and separated from other cells
Embryonic stem cells are removed from 5-day-old embryos
Cells are manipulated to stimulate them to take on a specific function
Specialised cells may then be used to treat unhealthy areas
"Not every day do we have the opportunity to vote to heal the sick," Democrat Senator Claire McCaskill said, describing it as "a noble cause".
Speaking before the vote, however, a White House spokeswoman said the president would veto the proposed bill because it "crosses a moral line that would use taxpayer dollars to destroy human embryos".
The process of extracting stem cells from an embryo destroys that entity; and conservative Republicans have likened the destruction of frozen human embryos to abortion.
Mr Bush imposed restrictions on spending government money on stem-cell research when he came to power in 2001.
He limited the offer of federal funds to research on stem-cell batches that were already available that August and ruled out funding work on fresh batches.
The president has instead offered to fund an alternative form of research which uses cells taken from amniotic fluid, placentas and from embryos that have died naturally.
The Senate passed a bill endorsing funding for such research later on Wednesday.