The aim of this study was to examine the immunomodulating effects of rhIL-12 on the immune response induced by hepatitis B virus (HBV) antigens in clinical subgroups of patients with HBV infection. Peripheral blood mononuclear cells (PBMC) of 80 patients were stimulated with HBsAg, HBcAg, pre-S1Ag and tetanus toxoid in the absence or presence of IL-12 (0.01, 0.1 and 1 ng/ml). Stimulation by anti-CD3+ anti-CD28 and lipopolysaccharide (LPS) were used as controls. Proliferation and cytokine production were determined by 3H-thymidine uptake and ELISA after 72 h. After stimulation with HBV antigens only, production of tumour necrosis factor-alpha (TNF-alpha) or IL-10 was observed in all patients, while interferon-gamma (IFN-gamma) was detectable in only 27 patients. After costimulation with IL-12 and HBV antigens, however, large amounts of IFN-gamma were found in all patients, while HBV-induced IL-10 production remained mostly unchanged. When clinical subgroups including patients with compensated liver cirrhosis were compared, PBMC from patients with HBeAg+ hepatitis showed the lowest capacity to produce IFN-gamma after HBV antigen-positive IL-12. These data suggest that the ability of IL-12 to enhance IFN-gamma production against HBV antigens is correlated with the presence of HBeAg and is not impaired in patients with advanced liver disease. In addition, IL-12 and IL-10 production by antigen-presenting cells may be a critical factor that determines the efficacy of the immune response against the hepatitis B virus.