Inclusion Criteria:

   - Subjects must have an HIV RNA level below the limit of quantification (e.g., <75
   copies, <50 copies, or <48 copies/mL, depending on the assay used) for at least 6
   months excluding "blips" (e.g., a single measurement between 48-200 copies/mL preceded
   and followed by measurements below the limit of quantification) while on
   antiretroviral therapy.

Exclusion Criteria:

   1. Completed treatment for any acute systemic infection (other than HIV-1) less than four
   weeks before study entry.

   2. Any active brain infection (except for HIV-1), brain neoplasm, or space-occupying
   brain lesion.

   3. Receipt of immunomodulating medication (e.g., corticosteroids, immunoglobulin, etc.)
   within four weeks of study entry.

   4. Any active psychiatric illness including schizophrenia, severe depression, or severe
   bipolar affective disorder that, in the opinion of the investigator, could confound
   the analysis of the neuropsychological test results.

   5. Active drug or alcohol abuse that, in the investigator's opinion, could prevent
   compliance with study procedures or confound the analysis of study endpoints.

   6. Unable to provide informed consent