The human immunodeficiency virus (HIV), widely acknowledged to be the cause of AIDS, is most commonly spread through the sharing of contaminated needles by intravenous drug users, semen during sexual intercourse, and from mother to child during pregnancy or delivery. Although the virus is often transmitted during homosexual sex between men, an increasing number of women are contracting HIV by means of heterosexual intercourse. In 1996, 40 percent of the women who were diagnosed with HIV were infected through heterosexual intercourse.

AIDS activists and researchers advocate the use of condoms as a prevention method, but condoms are not an option for many women whose male partners refuse to use them. However, women may soon have a new alternative to condoms—microbicides, chemical compounds that are inserted into the woman’s vagina in the form of a gel or suppository. Microbicides...