It remains uncertain whether hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) and pregenomic RNA (pgRNA) can be detected in the serum or peripheral blood mononuclear cells (PBMC) of patients with chronic hepatitis B (CHB) infection. We examined HBV cccDNA and pgRNA in the serum and PBMC, and investigated the effect of lamivudine therapy on the viral loads in the PBMC of CHB patients. Paired serum and PBMC samples from 50 treatment-naïve CHB patients [25 hepatitis B e antigen (HBeAg) positive and 25 HBeAg negative] were quantified for total HBV DNA, cccDNA and pgRNA by real time polymerase chain reaction. HBV cccDNA and pgRNA were below the lower detection limit in all serum samples, and in 84% of PBMC. HBV DNA (r = 0.889, P < 0.001) and pgRNA (r = 0.696, P < 0.001) in PBMC correlated with the HBV DNA in serum. In the longitudinal study, 30 patients treated with lamivudine therapy for a median duration of 34 weeks (range 12-48 weeks) were examined. The median HBV DNA reduction in PBMC before and after treatment was 1.318 (range -0.471 to 3.846) log units, which was significantly lower than serum HBV DNA reduction [3.371 (range -0.883 to 9.454) log units, P < 0.05]. HBV cccDNA and pgRNA were undetectable in the serum of CHB patients. HBV viral loads in PBMC correlated with serum HBV DNA. Lamivudine therapy had less effect on the HBV viral loads in PBMC compared with the serum viral loads.