The magnitude and breadth of T-cell responses against HCV are associated with the outcome of HCV infection. Parameters of HCV-specific T-cell responses that are frequently assessed in clinical immunological studies include proliferation of T cells in response to HCV antigens, frequency of HCV-specific T cells secreting cytokines, and changes in antigen specificity during the course of HCV infection. Common techniques for assessing these parameters such as 3 H-thymidine incorporation assay, cytokine ELISpot assay, and strategies for epitope mapping and identification of minimal optimal epitopes are outlined, and detailed protocols are described.