We propose to perform this study in two study populations. Cohort 1 will be comprised of 25 HSV-2 seropositive, HIV seronegative adults, and Cohort 2 will be comprised of 25 HSV-2 seropositive, HIV seropositive adults with a CD4 count>250 cells/mm3. As suppression of HSV-2 using acyclovir is currently being studied in large, multi-center, international clinical trials as an HIV prevention strategy, these results will have broad implications for public health around the world.