In the last several years, human embryonic stem cell research has continually popped up in policy debates on state and federal levels.

There are generally two main issues debated: Should it be allowed? And if so, should it receive government research funding?

In 1995 -- three years before the first reported isolation of human embryonic stem cells -- Congress placed a ban on government-funded research on human embryos. The ban was in place for six years, which meant none of the scientists conducting the earliest research on embryonic stem cells received any funding from the federal government.

After Dr. James Thomson's work at the University of Wisconsin in 1998, government officials began to rethink the ban on human embryo research. The Department of Health and Human Services drafted new guidelines for federal funding, concluding that public funds could be used for research on embryonic stem cells as long as the cells were derived with private funds -- thereby skirting the issue of government funding for the destruction of embryos.

After reviewing a flood of comments, the National Institutes of Health released the final guidelines on Aug. 25, 2000. With the backing of President Bill Clinton, the NIH solicited applications for its first embryonic stem cell research grants.

The NIH received several grant applications, and a committee was appointed to review the proposals. But before any applications were reviewed or money allocated, President George W. Bush came into office. Although Bush had spoken out against federal funding for the research during his presidential campaign, he didn't overturn the guidelines outright. Instead, he ordered a review by Secretary of Health and Human Services Tommy Thompson.

Current Federal Policy

On Aug. 9, 2001, Bush announced his decision on federal funding for embryonic stem cell research in an address to the nation. He said only research on stem cell lines already in existence by the time of his speech would be eligible for federal funding.

He said research on these stem cell lines was permissible because an embryo had already been destroyed. But federal funding would not be allowed for research on any stem cell line created after Aug. 9, 2001, as to discourage future embryo destruction. However, privately funded human embryonic stem cell research has remained permissible on either the “existing” human lines or on lines derived after August 9, 2001.

At the time of the address, the National Institutes of Health determined that there were 64 stem cell lines in existence. However, researchers have expressed doubts about how many lines are actually available for use, whether the cells provided enough genetic diversity and whether the lines are contaminated with animal cells. On Sept. 5, 2001, Thompson acknowledged that only 24 or 25 of the cell lines were established embryonic stem cell lines.

On Nov. 7, 2001, the NIH Human Embryonic Stem Cell Registry was launched. It lists all the cell lines that are eligible for federally funded research, as well as contact information for researchers who wish to use them.

There are currently no federal limits on private embryonic stem cell research, but some state laws restrict not only private funding but research on human embryos altogether, according to the National Conference of State Legislatures. South Dakota, for example, forbids all research on embryos outside of a woman's body.

Since Bush's address, the public has debated the current federal policy. Proponents of research find the policy far too restrictive, while critics say no such research should take place under any circumstances, much less federally funded research.

Since 2001, embryonic stem cell research has appeared in news headlines again and again as politicians publicize their views and celebrities -- including Michael J. Fox and the family of former President Ronald Reagan -- continue to push for additional federal funding.

In July 2005, a bill to expand stem cell research funding cleared the U.S. House of Representatives amid a presidential veto threat. But the bill didn't make it to a Senate vote despite Senate Majority Leader Bill Frist's announcement that he supports expanded federal funding. Although Frist had voiced this position in 2001, he had then expressed support for Bush's 2001 federal funding policy -- so Frist's public push for expanded funding in the summer of 2005 was reported by the media as a "break with Bush" on the issue.

Although the issue is expected to come up again at a federal level, Bush has said repeatedly that he doesn't support any further funding of embryonic stem cell research. But under the current policy, the NIH will continue funding research on human embryonic stem cell lines that are listed on the federal registry.

• Aug. 9, 2001: Transcript Of Bush's Address
• NIH: Human Embryonic Stem Cell Registry
• AAAS Policy Brief: Stem Cell Research