This is a cross-sectional study that will enroll 25 HIV-positive subjects on long-term d4T treatment with symptomatic peripheral neuropathy, 25 HIV-positive subjects on long-term d4T treatment without peripheral neuropathy, 50 HIV-negative subjects without peripheral neuropathy and 25 HIV-positive subjects on long-term d4T treatment with asymptomatic peripheral neuropathy for a one-time assessment.