The bill would now prohibit people from donating embryos for research.

Some clinics routinely ask patients if they want to donate embryos for research.

Each patient who has agreed to donate embryos must be contacted and agree to the particular stem cell project.

At Columbia University's fertility center, only two patients so far have asked about donating frozen embryos for stem cell research.

The guidelines include several provisions designed to discourage anyone from donating embryos for profit or the medical benefit of relatives.

In the United States, those donating embryos must, if possible, be screened for a series of infectious diseases.

People who donate embryos, in contrast, provide almost none of this information.

Ms. Andrews noted another problem with donating embryos: the donor couple may decide to seek custody or at least visitation rights.

Until recently, the principal source of human embryonic stem cells has been donated embryos from fertility clinics.

Second, that individuals donating embryos should do so freely, with voluntary and informed consent.