To understand the pathogenesis of chronic hepatitis B virus (HBV) infection, we examined the serum levels of IL-10, TNF-alpha IL-12 p70, and IL-12 p40 in 77 patients chronically infected with HBV and 19 controls. The patients were classified into four groups: asymptomatic carriers (ASC), patients with chronic hepatitis (CH), patients with liver cirrhosis (LC), and patients with hepatocellular carcinomas (HCC). The cytokine values among these groups were compared and their relations to clinical parameters were investigated. All these cytokine values were higher in the patient groups than in controls. IL-10 and TNF-alpha became higher in accordance with the progress of the disease phases, from ASC to LC, and lowest when the patients had HCC. IL-12 p40 was also lowest in HCC, however, the group with highest levels was CH. IL-12 p70 was unchanged among ASC, CH, and LC, but were raised in HCC. Serial analyses for the cytokine values in the same patients showed the similar tendencies. Regression analysis showed the significant correlations between ALT and IL-10. Serum cytokine values well reflected the pathological differences of the individual disease phases, and may become useful indices to understand the pathogenesis of chronic HBV infection.