Analysis of HBV-Specific Immune Response in Patients With HBeAg Negative Chronic Hepatitis B Treated With Pegasys (Peginterferon Alfa-2a (40KD)) - Immunology Sub-Study of ML18253

Inclusion Criteria: * Adult patients 18-55 years of age * Chronic HBeAg negative hepatitis B * Liver disease consistent with chronic hepatitis documented by liver biopsy within 18 months prior to enrollment * Participation in study ML18253. Exclusion Criteria: * Interferon-based or any systemic anti-HBV therapy \</= 12 months prior to first dose of study drug * Antiviral, anti-neoplastic, or immunomodulatory treatment \</= 12 months prior to first dose of study drug * Nonresponders to previous interferon therapy and resistant to lamivudine * Co-infection with hepatitis A, C or D, or with human immunodeficiency virus (HIV) * Hepatocellular cancer * Compensated (Child A, score 6) or decompensated liver disease (Child B or C) * History or evidence of medical condition associated with chronic liver disease other than HBV