To evaluate the improved sensitivity of 3rd-generation assays for the detection of ani-HCV antibodies in diagnosing cases of HCV infection, we have re-tested by 3rd-generation ELISA test (ELISA-3) serum samples from immunocompetent patients with chronic hypertransaminasemia who were HCV-RNA positive but tested negative with 2nd-generation ELISA (ELISA-2). Out of 21 HCV-RNA positive/ELISA-2 negative samples, 3 (14.3%) were ELISA-3 positive. Among the ELISA-3 reactive samples, two were indeterminate by RIBA-3 (one was reactive with c1 00 and the other with c22), and one was negative. These results demonstrate that even in the clinical setting ELISA-3 improves the diagnosis of HCV infection. The improvement seems to be related to a better reactivity of HCV peptides rather than to the inclusion of the new determinant NS5. However, the sensitivity of the tests for the detection of anti-HCV antibodies remains to be improved.