In that process, where fertilization occurs outside the woman's womb, excess embryos are often created and used in research.

Fertility centers discard relatively few excess embryos.

Couples may direct the clinics to donate their excess embryos for research, or to keep them frozen indefinitely, or to destroy them.

Already, some scientists are delicately trying to negotiate with fertility doctors to obtain excess embryos.

Dr. Muasher said that "99 percent of couples want to freeze their excess embryos."

In practice the cells come from excess frozen embryos due to be discarded by fertility clinics.

"I thought it was going to be a wonderful way for solving a real quandary for these couples who were wondering what to do with their excess embryos."

After all, the excess embryos would be discarded anyway.

But the same argument could be made against fertility treatments that create excess embryos bound for destruction, which is the common practice in this country.

Right now, the excess embryos are usually discarded, a practice that proponents of embryo research denounce as wasteful and even immoral.