Participants in this study will be randomly assigned to receive one of four interventions: BufferGel, PRO 2000/5, placebo gel, or no gel. All participants will receive HIV risk reduction counseling, condoms, and diagnosis and treatment of sexually transmitted diseases. Participants in the three gel arms will be given single-use, prefilled applicators of gel and will be instructed to apply one dose of the product (BufferGel, PRO 2000/5, or placebo gel) intravaginally up to 60 minutes before each vaginal intercourse while in the study.