Participants will be enrolled for 12 months in this study and will be randomly assigned to one of two study arms. The first arm will receive 400 mg acyclovir twice daily; the second arm will receive placebo. Follow-up visits will occur monthly. Participants will be tested for STDs, including HIV and syphilis, at each visit and treated as necessary; participants will also be given adherence and condom counseling, risk behavior and sexual history questionnaires, and genital symptoms questionnaires at all study visits. Medical history will be assessed and participants will undergo blood work at Months 3, 6, 9, and 12.