We analyzed the relationship between virological response and baseline immune factors in 17 patients chronically infected with hepatitis C virus (HCV) who received interferon-alpha-ribavirin therapy for 26 weeks. The number of intrahepatic CD8(+) cells present in the portal tract before the start of treatment was found to be significantly higher in patients who responded to treatment than in nonresponders. The relationship between portal CD8(+) cell counts and the response to therapy could be described by a logistic curve. Neither peripheral cytokine levels nor HCV-specific T cell reactivity in peripheral blood mononuclear cells showed a relationship to response to therapy.