The Senate opens a new debate over stem-cell research, as three bills are under consideration. One would overturn President Bush's restrictions on research. The president is expected to use his first-ever veto if that bill passes.
More likely to take effect, observers say, are two other bills meant to define the scope of research.
One would outlaw so-called "fetus farming," the creation of embryos that would be destroyed for research -- a method not currently in practice.
Another bill would encourage research into alternative ways to develop the properties of stem cells without destroying embryos now in existence.