President Bush and Democratic challenger John Kerry differ sharply on the controversial subject of embryonic stem cell research.
Scientists say the research could lead to treatments for a wide variety of diseases, including Parkinson's and Alzheimer's. But embryonic stem cell research has many opponents, because embryos must be destroyed before they are harvested for use in a "stem cell line" - a population of cells able to renew itself for a long period of time outside the body.
President Bush says he values exploring the promise of stem cell research while, in his words, "maintaining respect for all human life." In 2001, he endorsed federal funding for stem cell research, but restricted it to a small number of existing stem cell lines where the embryo had already been destroyed.
Mr. Kerry supports lifting bans on stem cell research, saying if elected he will support federal funding for research on new stem cell lines. Mr. Kerry says currently there are only 19 stem cell lines available for research -- far fewer, he says, than needed. He also says the research is supported by a bi-partisan majority of U.S. senators, as well as a majority of Americans.