At any given time in America, nearly 100,000 people are waiting for an organ transplant. Yesterday a chilling story in The Boston Globe demonstrated how desperate the ill can become, lingering on the waiting list for years. Two patients, a 57-year-old man and a 70-year-old woman, each agreed to accept a kidney from a deceased donor whose organs were approved under new "expanded" criteria. The kidneys they received came from a 49-year-old homeless man.

The tight transplant timetable and the cost of running the multitude of tests that can now be performed means that most organs are tested only for some of them - AIDS and hepatitis, for example. The homeless donor, however, carried a rare virus that is usually found in rats. The female transplant patient died and, as of yesterday, the male patient was fighting for his life.

When the alternative is death, most patients and most medical professionals are willing to gamble. At least one study has found that recipients who are older and people who received organs approved under the expanded standards - like those from an older donor or someone with high blood pressure - face only a slightly elevated risk.

Medical progress ensures that organ demand always outstrips the supply. That's creating ethical dilemmas that need to be resolved. It is illegal to sell a human organ but legal to donate one.

It is permissible to specify the recipient of one's organ, allowing that person to jump ahead of others whose time may be shorter. But people often advertise widely for an donated organ using a particularly poignant story that may or may not be accurate. Should they be allowed to shortcut the process designed to make sure that organs go to those whose need is most urgent?

Should it be illegal to sell a human organ? The director of bioethics studies at the libertarian Cato Institute and others with faith in market solutions to problems believes that it should be, given informed consent. If it saves lives, and it no doubt would, shouldn't the sale of an organ or organ tissue be allowed?

To increase the supply of viable organs for transplant, the meaning of death is being reclassified to include not just "brain death" but cardiac arrest. There is, however, disagreement over how long a person's heart must remain stopped before death can be declared and organs removed.

These questions will take on added urgency as baby boomers age and more older patients seek and benefit from organ transplants. But an end to such dilemmas is looking more likely all the time.

Scientists have grown skin, bone, cartilage and blood vessels for transplant in patients. In 2006, Boston researchers successfully grew and implanted tissue that formed roughly half the bladders of seven young patients. And this year, a University of Minnesota research team revealed that it had taken the valves and "architecture" of a heart from a dead rat that had been scrubbed of all its cells and seeded it with cells from a newborn rat. Within months, in a petri dish in their lab, a new rat heart was beating and pumping a small amount of blood.

The feat, Dr. Doris Taylor told The New York Times, "opens the door to this notion that you can make any organ: kidney, liver, lung, pancreas - you name it and we hope we can make it."

For tens of thousands of people, that day can't come soon enough. In the meantime, unless many more people sign up to be organ donors, the only hope for some patients lies in accepting an organ from a homeless donor.