At present there is no standard spproved treatment with demonstrated efficacy for children with chronic hepatitis B. In adult patients, lamivudine has been associated with a rapid, consistent and effective suppression of hepatitis B virus replication and improvements in liver histology. Lamivudine has been shown to prevent progression to more advanced stages fo fibrosis in the majority of treated patients. The objective of this study is to compare the efficacy of lamivudine versus placebo in children with Chronic hepatitis B with regard to complete virologic response and sustained normalization of serum alanine aminotransferase levels at one year. The safety of lamivudine will also be evaluated.