In murine models, overexpression of interleukin (IL)-12 and interferon (IFN)-γ can induce severe liver damage, whereas IL-10 has anti-inflammatory and hepatoprotective properties. To analyze the potential role of these cytokines in human fulminant hepatitis B, we used immunohistochemistry to study expression of IL-12, IFN-γ, and IL-10 in explant livers of 11 patients with fulminant hepatitis B, 5 patients with fulminant hepatitis due to other etiologies, 37 patients with chronic liver disease (CLD; hepatitis B virus, n = 15; hepatitis C virus, n = 10; primary biliary cirrhosis, n = 12), and 10 normal controls (NCs). Furthermore, cytokine messenger RNA (mRNA) levels were determined in the liver specimens by quantitative real-time polymerase chain reaction (PCR). In NCs, faint IL-12 expression was detected in only a few Kupffer cells, whereas sinusoidal endothelial cells, hepatic stellate cells, bile ducts, and lymphocytes expressed IL-12 in CLD and, more conspicuously, in fulminant hepatitis B. In contrast, expression of IFN-γ and IL-10 was restricted to lymphocytes and Kupffer cells, respectively. In fulminant hepatitis B, numbers of IL-12– and IFN-γ–positive cells markedly exceeded those found in CLD and NCs. A close correlation existed between IL-12 and IFN-γ expression (r = 0.68; P < .001). In contrast, IL-10 expression was not significantly different in CLD and fulminant hepatitis. The quantitative differences in immunohistologic cytokine expression closely corresponded to the mRNA levels. In conclusion, our data indicate massive induction of the proinflammatory cytokines IL-12 and IFN-γ in fulminant hepatitis B, which is apparently not counterbalanced by the anti-inflammatory cytokine IL-10. This cytokine imbalance may play an important role in promoting inflammatory reactions leading to massive liver damage in fulminant hepatitis B.