A vaginal microbicide containing a drug normally used to treat HIV is safe for sexually active HIV-negative women to use every day over an extended period. The trial of tenofovir topical gel also found most women adhered to a daily or sex-dependent regimen. The findings are a boost to HIV prevention efforts focused on “next-generation” microbicides to curb infection rates in women, most of whom get HIV through sex with their husbands or steady partners.