It is hard to find an economist who agrees with this policy. Gary Becker and Julio Jorge Elias argued in a recent paper that "monetary incentives would increase the supply of organs for transplant sufficiently to eliminate the very large queues in organ markets, and the suffering and deaths of many of those waiting, without increasing the total cost of transplant surgery by more than 12 percent."

Some noneconomists may well find this reasoning repugnant. There are many reasons, after all, for banning the sale of organs. Some people consider it immoral to commodify body parts (although it is now commonplace to not only sell sperm and eggs but also to rent a womb). Others fear that most organ sellers would be poor while most buyers would be rich; or that someone might be pressured into selling a kidney without fully understanding the risks.

But why, Becker and Elias ask, should poor people "be deprived of revenue that could be highly useful to them"? Even more compelling is the fact that a poor person is just as likely as a wealthy person (if not more so) to need a new kidney — and, with no legal market for organs, is just as likely to die while waiting on a list.

Alvin Roth, even though he is an economist, is smart enough to realize that repugnance will keep Americans from embracing a true market for organs anytime soon. So, along with several other scholars and medical personnel, he has helped design a clever alternative, the New England Program for Kidney Exchange. Imagine that you have a wife who is dying of renal failure, and that you would give her one of your kidneys, but you are not a biological match. Now imagine that another couple is in the same bind. The kidney exchange locates and matches the couples: you donate your kidney to the stranger's wife, while the stranger gives his kidney to your wife; the operations are performed simultaneously to make sure no one backs out. Although this system has yielded only a couple dozen transplants so far, it illustrates an economist's understanding of incentives: if you can't get someone to give an organ out of altruism, and you can't pay him either, what do you do? Find two parties who are desperate to align their incentives.

Otherwise, who in his right mind would step forward to donate a kidney to a stranger? In fact, we recently spoke to one such potential donor who asked to remain anonymous. Donor is married, with four children and a precarious financial situation. Because Donor had a sibling who nearly needed an organ transplant, the idea got into Donor's head to perhaps sell a kidney to a stranger. Through a donor Web site, Donor met a potential recipient, whom we'll call Recipient. It wasn't until the process was well under way that Donor learned it was illegal to be paid. In the end, however, Donor's moral mission overrode the financial need, and Donor decided to go ahead with the transplant.

Donor has undergone extensive testing at the hospital where Recipient will have the transplant. Both Donor and Recipient have had to lie repeatedly to the doctors, pretending they are old friends. "If they find out you met on the Internet," Donor explains, "they assume it's for money, and they'll call off the operation."

If all goes well, the transplant may happen soon. Consider the parties who stand to profit from this transaction: Recipient, certainly, as well as the transplant surgeons, the nurses, the hospital, the drug companies. Everyone will be paid in some form — except for Donor, who not only isn't being paid but, in return for carrying out a deeply altruistic act, also has to pay the additional price of lying about it.

Surely there are some people, and not just economists, who would find this situation — well, repugnant.