An autologous in vitro model was developed to analyze the immunologic cause of liver tissue injury during hepatitis A virus (HAV) infection. Human T lymphocytes infiltrating the livers of two patients with acute HAV infection were isolated from liver biopsy cores, cloned, and expanded in vitro. Procedures using a cell culture system with HAV-infected autologous skin fibroblasts demonstrated that 42% and 53% of the liver-infiltrating CD8⁺ clones were HAV-specific and that they kill HAV-infected skin fibroblasts in a human leukocyte antigen-restricted manner. Data show virus-specific killing by liver-infiltrating T lymphocytes in man and support the hypothesis that liver cell injury in acute HAV infection is mediated by HAV-specific CD8⁺ T lymphocytes and is not caused by a cytopathic effect of the virus itself.