JACKSON, Miss. - A debate is unfolding over an unusual offer from Mississippi's governor: He will free two sisters imprisoned for an armed robbery that netted $11, but one sister's release requires her to donate her kidney to the other.

The condition is alarming some experts, who have raised legal and ethical questions. Among them: If it turns out the sisters aren't a good tissue match, does that mean the healthy one goes back to prison?

Gov. Haley Barbour's decision to suspend the life sentences of Jamie and Gladys Scott was applauded by civil rights organizations and the women's attorney, who have long said the sentences were too harsh for the crime.

The sisters are black, and their case has been a cause celebre in the state's African American community.

After 16 years in prison, Jamie Scott, 36, is on daily dialysis, which officials say costs the state about $200,000 a year.

Barbour agreed to release her because of her medical condition, but the release order for Gladys Scott, 38, says that one of the conditions she must meet is to donate the kidney within one year.

The donation idea was Gladys Scott's, and she volunteered to do it in her petition for early release.

National NAACP President and CEO Benjamin Todd Jealous thanked Barbour on Thursday after meeting him at the state capital, calling his decision "a shining example" of the way a governor should use the power of clemency.

Others aren't so sure.

Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania, has studied transplants and their legal and ethical ramifications for about 25 years. He said he has never heard of anything like this.

Even though Gladys Scott proposed the idea and volunteered to donate the kidney, Caplan said, it is against the law to buy and sell organs or force people to give one up.

"When you volunteer to give a kidney, you're usually free and clear to change your mind right up to the last minute," he said. "When you put a condition on it that you could go back to prison, that's a pretty powerful incentive."

So what happens if she decides, minutes from surgery, to back off the donation?

"My understanding is that she's committed to doing this," said Barbour's spokesman, Dan Turner. "This is something that she came up with. This is not an idea the governor's office brokered. It's not a quid pro quo."

What happens if medical testing determines that the two are not compatible for a transplant? Turner said that the sisters were a blood-type match but that tests to determine tissue compatibility still needed to be done.

If they don't match, or if she backs out, will she be heading back to prison?

"All of the 'what if' questions are, at this point, purely hypothetical," Barbour said in a statement Thursday. "We'll deal with those situations if they actually happen."

Legally, there should be no problems since Gladys Scott volunteered to donate the kidney, said George Cochran, a professor at the University of Mississippi School of Law who specializes in constitutional matters.

Other experts said the sisters' incarceration and their desire for a transplant operation were separate matters and should not be tied together.

Michael Shapiro, chief of organ transplants at Hackensack University Medical Center in New Jersey and the chair of the ethics committee at the United Network for Organ Sharing, said: "If the governor is trading someone 20 years for a kidney, that might potentially violate the valuable consideration clause" in federal regulations.

That clause is meant to prohibit the buying or selling of organs, and Shapiro said the Scott sisters' situation could violate that rule because it could be construed as trading a thing of value - freedom from prison - for an organ.