(FORTUNE Magazine) – I saw the future of the AIDS epidemic on a recent visit to the teeming red-light district of Mumbai, a city of 12 million people. Here, in the commercial capital of one of the world's fastest-growing economies, thousands of sex workers --estimates range from 6,500 to 9,000--crowd the sidewalks, desperate to capture the attention of men who pay them a dollar or two. In a decaying school building that has been taken over by a nonprofit group that counsels sex workers, several former prostitutes told me that they used to service ten to 12 men each night, often in dormlike rooms shared by several women. Most of the sex workers are believed to be HIV-positive, but the men typically refuse to wear condoms. They return home and infect their wives, who pass the disease on to their children. It's a hellish mess, one that must be seen to be believed.

My guide in Mumbai was Bill Roedy, the president of MTV International who has become a leader in the global media campaign to fight AIDS. For Roedy, a West Point graduate and Vietnam veteran, the issue is personal. A close colleague at MTV became infected and died. "This is the defining moral issue of our time," he says. But MTV and its parent company, Viacom, have thrown themselves into the battle against AIDS for a pragmatic reason: More than half of new HIV infections hit people under 25. Left unchecked, AIDS will kill off MTV's audience.

So far more than 20 million people have died after being stricken with AIDS. Another 8,000 die every day. The epidemic shows no sign of abating. Nevertheless, most U.S. corporations have chosen to ignore the problem, and you can't blame them. AIDS has created business issues for pharmaceutical companies and a handful of global corporations, like Coca-Cola and ChevronTexaco, with significant holdings in sub-Saharan Africa. But since two-thirds of global AIDS cases are concentrated in a region that produces just 3% of the world's economic output, the disease has created a humanitarian catastrophe of little economic consequence. The epidemic has been irrelevant to most companies.

That is about to change. AIDS now threatens India, Russia, Ukraine, and China--nations too big for business to ignore. They are home to about 2.5 billion people, or 40% of the world's population. They aspire to be global economic superpowers. Their workers provide crucial links in the supply chains of multinational companies. If AIDS does to any one of those nations what it has done to Africa, the consequences for the global economy will be serious.

India has more HIV-infected people--somewhere around five million, although estimates vary widely--than any nation except South Africa. With 300 million poor people, massive numbers of migrant workers, and strong taboos against talking about sex and drugs, the Indian epidemic could spread rapidly. AIDS is growing faster in Russia and Ukraine than almost anywhere else, and the governments' responses have been entirely inadequate. As for China--well, we know that AIDS has contaminated blood supplies in rural China and infected sex workers in Shanghai and Beijing, but it's not yet clear how the government will respond. In a report titled "China's Greatest Challenge--Economic Development or AIDS?" Stephen Roach, the chief economist at Morgan Stanley, wrote, "All the economic growth in the world cannot possibly compensate for the devastation China would face" if the AIDS epidemic cannot be controlled. That's scary.

In 2003, five million people were infected with HIV, the virus that causes AIDS. That is more than in any year since its outbreak. "The epidemic, the virus, is still running faster than we are," says Dr. Peter Piot, the head of UNAIDS. "We are still losing the battle."

"HIV/AIDS directly threatens the security and prosperity not only of the highly affected countries but of our global society," declares Richard Holbrooke, the former U.S. ambassador to the UN who is now president of the Global Business Coalition on HIV/AIDS. And that is a problem for global business. "For business, the big message is that either you pay now or you pay later," says Dr. Helene Gayle, who runs the HIV, TB, and Reproductive Health Program of the Bill and Melinda Gates Foundation. "We know that. We've seen that."

Of course, governments, nonprofits, and the UN have the primary responsibility for fighting AIDS. But business has a role to play too. Companies can educate workers about AIDS and try to eliminate the stigma that remains a major obstacle to curbing the disease. They can provide treatment to employees. Perhaps most important, they can lobby governments to respond aggressively to the epidemic.

But not much of that is happening. Debra Dunn, senior vice president of global citizenship at Hewlett-Packard, says, "India is our largest employment site outside the U.S., but AIDS is not really on the agenda in the workplace yet." Last year the World Economic Forum surveyed more than 7,000 business executives in 103 countries about HIV/AIDS. About 21% said they expected HIV/AIDS to have a "serious impact" on their business. About the same percentage said they expected the disease to have a serious impact on their community. But only 6% of the firms said they had a written HIV/AIDS policy covering such topics as prevention, treatment, and discrimination in recruitment, promotion, or pay.

A few companies have joined the fight. Viacom shows AIDS-related messages on all its media properties. DaimlerChrysler provides extensive AIDS education and free HIV/AIDS drugs to its workforce. Rupert Murdoch's Star TV platform in India has teamed up with the Gates Foundation and actor Richard Gere's nonprofit to run a wide-ranging educational campaign in that country.

The good news is there's no mystery to this plague. The spread of AIDS can be stopped by changing human behavior. But that's easier said than done. If we can't get well-educated, affluent Americans to stop smoking and overeating, to exercise and use seatbelts, we know it won't be easy to get rural, poor, illiterate people in India, Russia, and China to change their sexual behavior and stop using drugs. The practices that spread AIDS have a web of underlying causes--poverty, lack of education, social instability, and gender bias against girls and women, who in desperation trade sex for money or gifts. Still, the complexity of the crisis is yet another reason for business to become involved. Problem solving is the essence of business. Businesspeople know how to get people to change their behavior, and they know how to deliver goods and services to those in need.

Not that there should be much debate over whether business--or the rest of us--should get involved. As William H. Gates (father of Microsoft founder Bill Gates) put it recently, "Many people make the case that AIDS is an economic issue or a national-security issue. That's all right with me. If we have to make that argument to get the public funds we need to fight disease, we should do it. But to me ... this is a humanitarian issue. People are dying, and we can save them. That ought to be enough."

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