Cytokines released by infiltrating T cells may contribute to the hepatic injury in chronic hepatitis. Therefore, we characterized peripheral blood- and liver-infiltrating T cells from patients with chronic hepatitis of different etiology and determined the T cell phenotypes and the cytokine release. Liver tissue and peripheral blood-derived T cells from patients with autoimmune hepatitis and primary biliary cirrhosis predominantly expressed CD4-molecules and the α- and β-chains of the T cell receptor (TCR). In chronic viral hepatitis B and C, liver- and blood-derived T cells were preferentially CD8+ T cells expressing the αβ TCR. Mitogenic stimulation with irradiated Daudi lymphoma cells and phytohemagglutinin led to a strong release of interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α) and interleukin-2 (IL-2) by T cells in patients with chronic hepatitis and in healthy controls. T cells from patients with primary biliary cirrhosis and some patients with autoimmune hepatitis showed a significantly higher secretion of interleukin-4 (IL-4) and interleukin-10 (IL-10) than T cells from patients with chronic viral hepatitis or healthy controls. Histologic inflammatory activity did not correlate with the amount of cytokines released after mitogenic activation. In conclusion, liver tissue and peripheral blood T cells of patients with autoimmune hepatitis and primary biliary cirrhosis were dominated by CD4+ TCR αβ+ T helper/inducer cells, whereas in chronic viral hepatitis an enrichment of CD8+ TCR αβ+ cytotoxic/suppressor T cells was observed. In addition, analysis of the cytokine release showed that T cells in autoimmune and chronic viral liver diseases secreted high amounts of IFN-γ and TNF-α, cytokines predominantly secreted by Thl-like cells. The secretion of the Th2 cytokines. IL-4 and IL-10, however, was increased in autoimmune hepatitis and primary biliary cirrhosis. These data show that in autoimmune and chronic viral liver diseases different functional T cell subsets are activated.