The development of surrogates to predict HIV prevention product safety and efficacy is a high priority. An ex vivo challenge model is one such promising surrogate. Colonic tissue exposed to rectally applied microbicides in vivo and then challenged with HIV in the lab showed significant reduction in HIV replication when compared to tissue exposed to placebo gel. Currently, the ex vivo challenge model for ectocervical and vaginal tissue is being developed at the Dezzutti lab at the Magee Womens Research Institute in Pittsburgh, PA. Questions which need to be addressed in order to optimize the model include which HIV virus is most appropriate to use to challenge the tissue, is qPCR a more appropriate endpoint and marker of infection, and can frozen tissue perform as well as fresh tissue in the challenge model.