Although the major target organ for hepatitis B virus (HBV) is the liver, the possibility of infection of peripheral blood mononuclear cells (PBMCs) with HBV has also been reported. This study was performed to analyze the course of HBV infection of PBMCs and to investigate the influence of interleukin-6 (IL-6) on the efficiency of infection of PBMCs with HBV in vitro. PBMCs isolated from a healthy donor were infected by exposing to a HBsAg-, HBeAg-positive serum in the presence or absence of exogenous IL-6. The efficiency of infection was estimated by HBV DNA determination in the cells and medium in the course of infection. The results of this study show that the presence of IL-6 during the PBMCs infection with HBV increased the efficiency of this infection.