Background/aims: New methods to detect virus-specific T-cell responses have recently been developed. Several human leukocyte antigen (HLA)-peptide tetramers for the detection of hepatitis C virus (HCV)-specific CD8+ T cells are under evaluation. Methods: Evaluation of one HLA class I-tetramer (HCVNS3-2) for the detection of HCV NS3-specific CD8+ T cells in a series of 38 HLA-A2+ chronically infected patients. Results: Almost half (42%) of the patients had detectable NS3-specific CD8+ T cells. The frequencies of such cells ranged from 0.01% to 0.22% of total CD8+ T cells. No significant differences in clinical features or mean viral load were detected between patients with or without tetramer+CD8+ T cells. Conclusions: The tetramer HCVNS3-2 may be very useful for the study of the HCV-specific CD8+ immune response. Combination of this reagent with other tetramers based on other HCV peptides may help in the understanding of the immune response to the virus. However, a panel of tetramers based on several parts of the HCV polyprotein may be a mandatory requirement to explore the whole breadth of the CD8+ T-cell response against HCV and to detect that response in the majority of patients with chronic infection.