A new approach to HIV prevention currently being studied includes the use of microbicides, substances that kill microbes. Tenofovir disoproxil fumarate (TDF) is an oral, FDA-approved, anti-HIV drug, and tenofovir gel is an experimental microbicide. The purpose of this study is to determine the adherence and acceptability to and blood levels of three daily regimens of tenofovir in both oral and gel form.