The MTN-003 HIV prevention study include the use of microbicides, substances that kill microbes, and tenofovir disoproxil fumarate (TDF) and emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) - oral, FDA-approved, anti-HIV drugs. The purpose of this study is to determine if taking daily TDF and FTC/TDF as a part of the study MTN-003 has an effect on bone mineral density (BMD).

The effect of tenofovir on bone mineral density (BMD) has not yet been studied and is of potential concern. The purpose of this study is to determine the changes in BMD among individuals receiving TDF and FTC/TDF compared with a placebo.

This substudy will enroll individuals currently participating in MTN-003. The expected duration of participation for each participant is approximately 48 months. Study treatment will be provided by MTN-003. Study treatment will not be provided by this substudy.

Study visits will occur every 6 months after enrollment. A nutrition assessment, physical activity history, and urine and blood collection will occur at all visits.

Inclusion Criteria:

• Enrolled in MTN-003
• Randomized to oral study product in MTN-003 within 14 days prior to study entry

Exclusion Criteria:

• Medical condition known to affect bone or taking any medication known to affect bone. More information on this criterion can be found in the protocol.
• Permanently discontinued from oral study product in MTN-003 prior to study entry
• Any condition that, in the opinion of the investigator, would interfere with the study
• Pregnant

Sexually active, HIV-uninfected women who are currently enrolled in MTN-003