This open-label, multi-center study will evaluate the effect on the quantitative HBsAg reduction of peginterferon alfa-2a [PEGASYS] in patients with HBeAg positive chronic hepatitis B. Patients will receive PEGASYS 180 mcg sc once weekly. After 24 weeks of treatment, rapid responders will receive another 24 weeks of treatment. After 24 weeks of treatment, slow responders will be randomized to another 24 or 72 weeks of PEGASYS monotherapy, or to 72 weeks PEGASYS plus 36 weeks adefovir (10 mg, po once daily, starting from week 29 of PEGASYS treatment). The anticipated time on study drug is >2 years.

Inclusion Criteria:

• Adult patients >/=18 years of age
• HBeAg positive chronic hepatitis B
• Compensated liver disease

Exclusion Criteria:

• Patients who had previously received treatment of drugs with activity against HBV within 6 months prior to study start
• Antiviral, anti-neoplastic or immunomodulatory treatment
• Co-infection with active hepatitis A, hepatitis C, hepatitis D, or HIV
• Evidence of decompensated liver disease
• Chronic liver disease other than viral hepatitis