Of all the wars in Africa, the most deadly is between humans and mosquitoes. More than a million Africans die of malaria every year, the vast majority of them small children. Malaria shrinks the economies of countries where it is endemic by 20 percent over 15 years. One reason the mosquitoes are winning is that the world had essentially discarded its single most effective weapon, DDT.

But Washington recently resumed financing the use of DDT overseas, and the dynamic new malaria chief of the World Health Organization, Arata Kochi, has said that the W.H.O., too, endorses widespread indoor house spraying with DDT.

This is excellent news for the humans in Africa. DDT both repels mosquitoes and kills them. It is the cheapest, longest lasting and most effective insecticide, and it will not threaten the ecosystem. Unlike in the past, DDT will now be sprayed inside houses once or twice a year in minute amounts.

DDT was the most important insecticide in the eradication of malaria in the United States, and in malaria control in southern Europe, Asia and Latin America. With DDT, malaria cases in Sri Lanka, then called Ceylon, dropped from 2.8 million in 1946 to 17 in 1963.

But Rachel Carson's 1962 book ''Silent Spring'' documented how DDT, sprayed over crops and over cities, built up in the ecosystem, killing birds and fish. William Ruckleshaus, the first head of the Environmental Protection Agency, banned DDT in 1972 for all but emergencies.

This was the right decision -- for the United States. Malaria was no longer an issue, and Washington needed to ensure that it would not be used on crops. But the decision had deadly consequences overseas. ''If I were a decision maker in Sri Lanka, where the benefits from use outweigh the risks, I would decide differently,'' Mr. Ruckleshaus told me in 2004. ''It's not up to us to balance risks and benefits for other people.''

Yes, except that Africa's malaria programs are financed by donors and vetted by the world's health establishment, which is dominated and financed by the United States and Europe, where DDT is also banned. People in rich countries felt it would be perceived as hypocritical to push a product in poor countries that they had banned at home. Even malariologists who knew DDT could be used safely dared not recommend it.

The United States, which used DDT irresponsibly to wipe out malaria, ended up blocking much poorer and sicker countries from using it responsibly. Under American pressure, several Latin American countries that had controlled malaria stopped using DDT -- and in most of them, malaria cases soared.

The other reason for DDT's demise was donor tightfistedness. DDT has to be sprayed inside houses, an activity that needs to be carried out by governments. In most African countries, this means donors must pay. They balked, and insecticide-treated bednets became bureaucrats' preferred solution. Donors liked the program because it was cheap and sustainable, as consumers would buy the nets -- often at subsidized prices. But it has failed. The nets work -- but even at $5, few can buy them. The most recent data show that only 3 percent of African children sleep under treated nets.

The eradication of malaria in rich countries turned out to be the worst thing that happened for people with malaria in poor countries. Malaria lost its constituency, and the money dried up. Throughout Africa, until recently, countries were using chloroquine to cure malaria, a medicine that cost pennies, and so could be bought by rural families. But mosquitoes had become resistant to it. And donors were unwilling to spend the money for effective medicines.

But this is changing. The AIDS pandemic has raised interest in third-world disease, and malaria financing has more than doubled in the last three years. African countries are also learning from South Africa, which doesn't have to depend on donors. Since 2000, South Africa has been successfully beating malaria using the new medicines and house spraying with DDT.

Conservatives in the Senate, led by Tom Coburn and Sam Brownback, have forced a revolution in Washington's malaria programs. America now promotes effective malaria drugs, gives away bednets, and has brought back house spraying -- including with DDT.

Malaria soared because the forces allied against it quit the battlefield. Now the humans are back.