TDF has been selected for investigation as prophylaxis against HIV in high-risk men because of its unique pharmacologic profile. In addition to the convenience of being a once daily single tablet, TDF’s safety profile is comparable to placebo among HIV infected persons, it has striking anti-HIV potency, and it has low potential for selection of resistant viruses. TDF is cleared from the body by the kidneys and is not metabolized by the liver. Therefore, TDF has limited potential to have pharmacokinetic interactions with other hepatically metabolized drugs. Each of these properties is necessary given the realities of the intended target populations. Moreover, initial prevention studies in simian models have provided encouraging results. Finally, the drug’s sponsor is supportive of investigating the potential use of TDF as a preventive, as well as therapeutic agent, will provide TDF for the study, and is willing to make a good faith effort to make TDF available for public health use should it prove to be effective for HIV prevention.