As capital markets stagger, it seems an odd notion. But Uncle Sam thinks private money can help solve some of the world's biggest health problems in areas where drug companies, already scrambling for new revenue streams, have long refused to tread.

Under a new Food and Drug Administration program, companies that develop treatments for a list of so-called tropical diseases in developing nations will receive an FDA voucher. A firm that brings to market a much-needed drug can redeem its voucher for a faster FDA review of another drug in its pipeline or sell the voucher to another company. This, theoretically, could make the vouchers a hot commodity in the drug world, where even six months'head start -- the time potentially saved by an FDA priority review -- can mean tens or hundreds of millions of dollars of extra sales. Or for small biotechs with relevant projects, the possibility of a voucher could attract bigger development partners.

"It would be a very valuable card to have," says Leslie Hudson, chief executive of AVI BioPharma Inc. in Portland, Ore., a firm whose pipeline includes treatments for the deadly Ebola and Marburg viruses.

The idea, which blossomed from academic paper to signed legislation in two years, echoes the carbon-credit exchange, which remains more concept than practice. Companies that cut pollution get gold stars, in effect, and can sell them to companies that must balance less-than-stellar records.

To trigger a voucher, the company's drug must gain FDA approval to treat a handful of tropical diseases that mainly affect poor people. Some are widespread, such as malaria; some are on the wane, such as the gruesome guinea worm disease, in which a parasite as long as three feet exits the body through an open wound. (Ebola and Marburg aren't on the list now.) Most are ignored by for-profit companies, because the victims can't afford medicine, nor can the countries where the diseases are endemic. HIV/AIDS doesn't count, because market demand in the developed world is high and companies have plenty of fiscal incentive to develop treatments.

With the FDA's draft of the plan released in October, the program is a work in progress. Observers want more clarity on why some diseases aren't included.

Already there are calls from the biodefense sector for the FDA to expand the list of voucher-eligible diseases. The FDA is listening -- it convened a meeting in December to let AVI and several others argue their cases -- but diseases that can double as bioweapons might already have enough attention in the post-Sept. 11 world, with billions of defense and homeland security dollars aimed at research and stockpiles.

"Is the government-created market for, say, anthrax [treatments] a significant market? It's something FDA may have to wrestle with," says Wendy Taylor, founder of BIO Ventures for Global Health, an arm of the biotech industry's trade association that is tracking the voucher program. "But we need to make sure the program works before expanding it."

FDA officials declined to say whether or when they would expand the list.

The first test should come soon. Swiss drug giant Novartis AG is waiting to hear from the FDA about Coartem, a malaria drug not yet approved in the U.S. There's no malaria risk in the U.S., but the firm wants to sell it to travelers heading abroad.

If approved, Coartem will likely earn Novartis a voucher that it can apply to any drug in its portfolio. A Novartis spokeswoman says the firm will apply the voucher to one of its products "that would meet a significant unmet medical need."

In other words, Novartis wants everyone to know it won't use the voucher for, say, yet another erectile dysfunction pill. Critics worry the program will trivialize the FDA priority review system, which is meant for drugs that fight diseases without good solutions.

To prevent priority-review bottlenecks, bearers who cash in their vouchers will pay an extra fee to help the FDA add reviewers and resources, at least theoretically. Missed deadlines are already plaguing the FDA.

It remains to be seen whether the lure of vouchers is enough to pull in smaller companies, especially in tough times.

Persuading investors to stay on board for years and fund expensive trials with the future possibility of a lucrative voucher -- one whose market value is far from guaranteed -- will be tricky.

"If you're on the board of a hotshot biotech and two researchers come up with two products, one a vaccine that prevents a major disease in a Third World country and the other an antibody that's 30% effective in rare tumors, the board will say, 'Let's go with the antibody,' " says Donald Francis, executive director of Global Solutions for Infectious Diseases. "It's hard to see stringing investment out that long for a voucher that may or may not come."

The program isn't aimed just at for-profit companies. At the Walter Reed Army Institute of Research in Silver Spring, Md., at least two late-stage drug programs might eventually qualify for a voucher, says Colin Ohrt, a colonel and clinical pharmacologist who specializes in malaria.

A voucher in hand, or the near promise of one, could help the institute attract private development partners, he says. "I think companies would be coming to us instead of us going out to look for them."

Like other potential participants, Ohrt wants to see several requirements of the program changed, including some he argues severely limit the number of malaria and tuberculosis treatments that qualify. With input coming from all sides, and the new Congress eager to press through major FDA reforms, the program -- essentially a voucher marketplace -- will no doubt evolve in the coming months. That might bode ill. As we've seen, markets don't do well with instability.