Finding a microbicide is one of the thorniest problems in AIDS research.

Women in poor countries need a vaginal gel that blocks the AIDS virus but not sperm because many still want children. They also need one that can be inserted secretly: for too many women, any action that implies that a partner is infected is likely to result in a beating.

And men who have sex with men may well need a microbicide that works rectally.

Previous trials of microbicides had to be stopped when they proved ineffective or even made women more likely to become infected. New research presented in Montreal last week suggested that progress is being made, but slowly.

In a study supported by the National Institutes of Health, a new gel called Pro 2000 was tested in 3,099 women in Africa and the United States. It appeared to protect them 30 percent better than a placebo, but researchers are awaiting results of a British study on 9,000 women.

Gels containing one or two antiretroviral drugs, tenofovir and FTC, were tested in monkeys. They appeared to give 100 percent protection  but researchers cautioned that only six monkeys got each gel, that the gels had high doses of drugs, and that what works with simian virus in monkeys does not always work in humans.