While many scientists search desperately for ways to cure AIDS, others have devoted their time to finding better ways to prevent the spread of the deadly virus that causes it - HIV. Condoms have been shown to be effective at blocking transmission of the virus between people. But in many parts of the world, men don't - or won't - use them.

Now new research is showing promise for a microbicide - a substance that kills HIV on contact. The idea behind a microbicide is to keep a woman from being infected when she has sex with an HIV-positive man.

"Microbicides are substances that can be applied in the vagina or rectum?  they are there to substantially reduce the risk of getting HIV," says Dr. Lameck Chinula, who works with the University of North Carolina at a site in Malawi.

"This is of great importance, especially in the setting of countries like Malawi, where most women are not so empowered that they can negotiate for condom use," Chinula says.

Chinula was part of an international team of scientists who are part of the Microbicide Trials Network.  Researchers in five countries gave microbicide gels to more than 3,000 women to use over a period of a year and a half.

During the study, women got either the active microbicide gel, another gel intended to block - but not kill - HIV, or an inactive gel.  The women were also given condoms, treatment for sexually transmitted diseases and instruction on how to prevent getting HIV.

"The idea is, you have a woman who would apply the gel if she thinks she will have intercourse with a man? in advance, or without actually asking the partner to put on a condom," Chinula says.

The first finding was that the gel did not increase a woman's chance of acquiring HIV. Some earlier attempts at microbicides had had that effect.

The most important finding is that the microbicide reduced the rate at which women contracted HIV.  Some of the women using the microbicide did get the disease, but they acquired it at a lower rate than other women in the study.

"We may not have enough evidence to say that they protect women from getting HIV," Chinula says.  "But I'm very optimistic these gels may offer some protection to women."

Chinula says these results add vital data to speed the development of an effective microbicide, which could give women a tool to protect themselves in the future.

The study results were announced at the annual Conference on Retroviruses and Opportunistic Infections in Montreal.