We have analysed the dynamics of HBV variants related to Lamivudine resistance in 22 chronically infected patients during and after the end of Lamivudine therapy. Thirteen patients had a confirmed methionine mutation in the YMDD region of the reverse transcriptase domain determined by sequence analysis. They responded to therapy having a mean reduction of HBV DNA of 4.55 log (range 2.93-8.91). Nine patients partly responded to therapy, with a small decline of HBV DNA (mean reduction of 3.39 log, range 1.72-5.12) and no indication for an YMDD variant. Samples were re-analysed with a HBV Drug Resistance Line Probe assay (InnoLipa HBV-DR), which detected as low as 10% of a variant HBV population. With this assay, changes in the YMDD region were detected with a mean of 2 weeks (range -8 to 10) earlier than by an increase of HBV DNA levels. Increase of ALT was observed with a mean of 31 weeks (range 29-51) later than the methionine changes in the YMDD motif. Indications for a methionine into valine change could be determined in only one of the partial responders. An unexpected observation was the predominant presence of variant virus populations after end of therapy. In ten patients, we detected the wild type virus with a mean of 14 weeks after end of therapy (range 1-42 weeks). In three patients, no variant virus population could be detected at 25, 36 and 37 weeks, respectively, after cessation of treatment. This observation is important for the inclusion of the so-called naive patients in clinical trials.