A vaginal gel has significantly cut the rate of women contracting HIV from infected partners in an experiment in South Africa, researchers said.
They said the gel, containing Aids drug tenofovir, cut infection rates among 889 women by 50% after one year of use, and by 39% after two and a half years.
If the results are confirmed it would be the first time that a microbicidal gel has been shown to be effective.
Such a gel could be a defence for women whose partners refuse to wear condoms.
New ways of curbing the spread of HIV are badly needed, particularly in sub-Saharan Africa, where nearly 60% of those infected with the virus are women.
Many women are often forced to take part in unsafe sex, and are biologically more vulnerable to HIV infection than men, making a gel they apply an attractive option.
Welcoming the results, UN agencies said they would convene an expert consultation in South Africa next month to discuss the next steps with the product.