To monitor the progression of lamivudine therapy by demonstrating HBV DNAs and RNAs in the serum of a chronically infected patient.Viral nucleic acids were extracted from serum samples taken during a 14-week treatment period and analyzed via competitive PCR and RT/PCR.The dynamic changes n the amount as well as in the structures can monitor therapy process very well.Our study indicated the level of polyadenylated viral RNA can be a marker for expression in general,and the appearance of replicative intermediates as a mirror of the mode of action of an antiviral drug.