Treating genital herpes can also help keep the AIDS virus under control in women with both infections, and might reduce the spread of HIV, too, the first major study to test this strategy suggests.

Many people with HIV are also infected with the herpes type 2 virus, and scientists have long known that herpes sores on the genitals can make it easier to become infected with the AIDS virus and could increase the risk of transmitting HIV to others.

In the latest study, conducted in Africa and published in Thursday's New England Journal of Medicine, women who took the herpes drug valacyclovir had less HIV in their blood and in their genital secretions.

The study did not look at whether the drug, sold as Valtrex by GlaxoSmithKline PLC, actually reduces transmission of the AIDS virus. However, scientists generally have found that the more virus someone has, the greater the risk of transmission.

Doctors have been looking for novel ways to treat and prevent HIV infection, particularly in poor countries where few can afford modern AIDS drugs and the stigma keeps many from taking them. Researchers recently found that circumcision lowers the risk of spreading HIV, and they hope the same will prove true of treating herpes.

"It does open some potential avenues to slowing down the HIV epidemic," said Dr. Lawrence Corey, a leading herpes researcher at the University of Washington who had no role in the study but has received research grants from Glaxo.

There are 40,000 new HIV infections in the U.S. each year and 4.3 million new cases worldwide. Previous studies have shown that herpes infections can triple a person's chance of acquiring HIV and can make HIV-positive individuals more infectious.

In the study, 140 women from the West African nation of Burkina Faso who were infected with the both the herpes and AIDS viruses received either valacyclovir or dummy pills for three months. Participants were not taking other AIDS medications.

Doctors took vaginal swabs and drew blood samples twice a week to measure HIV levels.

Those who took the drug ended up with less HIV in the bloodstream, with their count dropping from an average 20,000 virus copies per milliliter of blood to 8,000 copies. The placebo group saw their HIV levels spike, from an average of 50,000 virus copies per milliliter of blood to 63,000.

The treatment group was also less likely to have HIV in their genital tract — 13 percent had detectable virus levels during each visit, compared with 27 percent in the placebo group.

The study involved researchers from France, England and Burkina Faso and was funded by the French national AIDS research agency, ANRS.

One of the study's authors, Dr. Philippe Mayaud of the London School of Hygiene & Tropical Medicine, called for more research on herpes control methods, including the development of a herpes vaccine. Mayaud has received research support from Glaxo.

A larger study funded by the Bill and Melinda Gates Foundation is under way that aims to be the definitive word on whether treating herpes patients with acyclovir, the first herpes drug, can slow down HIV transmission.

Some AIDS specialists said it is unlikely herpes drugs will be the first line of defense against AIDS. However, they said such treatment could be useful in preventing HIV transmission in Third World countries without access to modern AIDS drugs.

"If, heaven forbid, we didn't have treatments for HIV, this would be something we would use. Fortunately, we have much better therapies to treat HIV," said Dr. Michael Saag, director of the AIDS Center at the University of Alabama at Birmingham. He has consulted for Glaxo.