As of now, it is illegal to buy kidneys from living donors in the United States. At the same time, most people on a waiting list for a transplant die before they get to the head of the line. The cost of keeping people on dialysis while they wait is tremendous, both in money and in the patient's diminished life and health. Some are proposing various incentives for living donation.
On the other hand, paying living donors for kidneys, as in some Third World countries, means that the people who donate are the ones who are desperate for money. In the precarious US health care system, you can see a situation in which people sell kidneys to pay off already-onerous medical debt. The poor should not become organ farms.
There have been several different schemes proposed for compensating living donors, from tax breaks to covering a wide range of expenses to paying cash. The studies show that even paying large sums of money to donors saves money in the long run compared to keeping patients on dialysis. Read about several of these proposals at Metafilter, and let us know your thoughts.
(Image credit: Scientific Animations)