The systemic administration of interferon-alpha (IFN-A) is associated with frequent and well characterized neuropsychiatric toxicity. The primary purpose of this study is to determine if treatment with IFN-A in combination with ribavirin alters human brain biochemistry as measured by proton magnetic resonance spectroscopy. The study population will be drawn from subjects simultaneously enrolled in a NIDDK protocol (98-DK-0003) that employs IFN-A and ribavirin for the treatment of hepatitis C virus (HCV) infection. Subjects will be evaluated prior to IFN-A/ribavirin treatment and then followed prospectively with the specific aim of identifying the emergence of central nervous system (CNS) effects. The principal outcome measures will be as follows: determinations of specific brain metabolites as measured by proton magnetic resonance spectroscopy (1H-MRS), a brief, non-invasive, and minimal risk procedure; ratings of mood, cognitive, and behavioral symptoms.