There will be a total of 8 study visits: 5 visits for Step I (including the entry visit) and 3 visits for Step II. Medical history will occur at all visits. Blood collection will occur at all visits. Participants who have positive nonreactive rapid plasma regain (RPR) values at screening will have mandatory lumbar punctures; for those with negative serum RPR results lumbar punctures are optional. Participants who test positive for syphilis will also have a lumbar puncture at their discretion to determine if syphilis has affected the brain. A neurological exam, other neuropsychological, dementia, and depression scale assessments, and urine collection will occur at most visits. Patients will be asked to complete a questionnaire on daily living at study entry and Weeks 12 and 24. Patients who have a lumbar puncture at Week 24 will receive a phone call 2 to 5 days after the procedure to report any adverse effects. Some participants may also have an electrocardiogram (ECG) during the study. For participants not on atazanavir some procedures and sample collections are optional.