On August 9, 2001, President Bush announced a policy that would allow federal funding for research done only on human embryonic stem cell lines established before that date.

On July 18, 2006, the Senate overwhelmingly passed a bill which would allow federal funding for research on already established embryonic stem cell lines. (The bill had already been passed by the House.) The following day, as promised, Bush vetoed this bill, exercising the first veto of his presidency, and Congress failed to obtain the two-thirds majority required to overcome the veto.

I assume that the president honestly believes it was necessary to veto the bill, despite the support for stem cell research by more than 60 percent of the American public as well as most federal lawmakers.

He stated his position: "This bill would support the taking of innocent human life. It crosses a boundary that our decent society needs to respect." However, it's also clear that the president's veto serves the important political aims of maintaining the support of the conservative right for him and other Republicans.

Quite frankly, I fail to understand how the president or the conservative right can view the use of cell lines established subsequent to 2001 as taking innocent human life. Nor can I understand how deriving new cell lines from leftover embryos slated for destruction at fertility clinics can be construed as taking human life.

Why not just use the cell lines allowed by the 2001 policy statement? Only 21 of the 64 approved lines are available at all for studies. However, there are substantial problems even with these cell lines. Many grow too slowly to be useful. Genetic mutations have accumulated as the cells have aged over the past five years. Finally, most were grown under conditions not compatible with their use in humans.

Another approach is to use stem cells derived from adults. Unfortunately, though such cells have been grown in laboratories, the supply is and will remain limited because they grow slowly and only for a short time.

Why are so many embryonic stem cell lines needed? Stem cells can be effective in the treatment of diseases only after they are converted to specific cell types, such as nerve cells to treat Parkinson's disease or pancreatic beta cells for type 1 diabetes. Studies have shown that some stem cell lines, but not others, can be converted into specific tissue cells.

U.S. scientists can still obtain non-federal funds to support embryonic stem cell research from companies, such as those in the pharmaceutical industry, and from funds provided by some state legislatures, most notably California.

But these funds are not enough to support the large number of scientists in this country poised to explore and apply the potential health benefits of stem cells.

Meanwhile, other countries, notably Sweden and Great Britain, are moving ahead with embryonic stem cell research, and the European Union (EU) has approved many billions of Euros for such research in EU countries.

In fact, it doesn't matter whether important medical breakthroughs are made in other countries around the world rather than in the U.S. However, such breakthroughs are more likely to occur sooner if the large number of scientists and laboratories in this country can join the effort.

Sooner is very important. Although much of the public has been sold on the potential benefits of stem cells in the fight against disease, it will probably take a number of years before these benefits have practical applications for improving people's lives. So it seems likely that the more scientists involved and the more stem cell lines available, the sooner we'll reap the medical rewards.