It's true that more "paired donations" such as those at Hopkins would shrink the queue.

Paired donations occur when a potential donor's kidney doesn't match his needy friend or relative but does match a stranger. If the stranger's donor matches up with the first patient, the parties can participate in a multi-kidney exchange. Such arrangements have been hindered, Hopkins officials say, because Congress hasn't explicitly allowed them. They want the law modified.

But why stop there? Even unfettered paired donations won't come close to meeting the need. At best they might double the 6,000 kidneys contributed annually by live donors.

Most people with failed kidneys have no live donor, compatible or otherwise. They must wait years for a transplant from a car-accident victim or other cadaver, which furnishes fewer than 10,000 kidneys a year. Each year 40,000 people join the waiting list.

Cash payments, which would need to be decriminalized by Congress, could break the logjam.

This is where you can start to squirm. I'm talking about "organ trafficking," peddling the tissue that God gave us for currency that could be exchanged for a widescreen TV. "My side is starting to ache," a friend said last week when I described the idea.

But legalized, closely regulated sales could not only close the kidney supply gap; they could offer salubrious competition to the shady, international black market that goes on now.

Donating a kidney is surprisingly low-risk - lower than that of childbirth. We are born with two kidneys, but one usually does the job. Decades later, donor mortality is no worse than that of the general population, studies show.

The biggest objection to legal kidney markets - and it's a good one - lies in the potential for social inequity. Rich folks buying harvested kidneys from poor folks who might need the money for rent is not a promising formula for civil society.

But there is already a glaring inequity in the status quo. Blacks are more likely than whites to languish for years on the waiting list. (Partly that's because they do better on dialysis.) Carefully controlled financial incentives could increase donations and help minority renal patients and everybody else disconnect from tubes.

"The argument is simple," says Dr. Arthur J. Matas, a prominent Minnesota transplant surgeon. "It's that patients are dying and suffering for lack of organs, and incentives could make a difference. And we should have some trials so we can find out."

Thoughtful proponents such as Matas don't want to sell used kidneys like Chevrolets. He suggests a government agency to fix a price, broker all donations, require lengthy counseling for donors and make insurers, not kidney recipients, pay donors.

"Four years ago this was an extremely radical position," he says. "Right now I would say that the tides are truly turning."

But only so far. Matas is careful to say he speaks only for himself, not for the American Society of Transplant Surgeons, of which he is president. Johns Hopkins wants nothing to do with the idea, citing "too many unresolved ethical issues."

"We are always interested in finding new strategies to help patients waiting for kidney transplants," Dr. Montgomery, director of the hospital's Comprehensive Transplant Center, said in a written statement. "However, the use of financial incentives for organ procurement is not one of them."

Too bad. The average kidney-transplant wait used to be about a year. It is now pushing five years. A pilot program might well convince us that the social and ethical costs of buying kidneys are greater than the social and ethical costs of letting thousands die each year. But we won't know until we try.\