Recently, the principal etiological agent of parenterally transmitted non–A, non–B hepatitis was molecularly cloned from the plasma of an experimentally infected chimpanzee. It was named hepatitis C virus (HCV). The first diagnostic test for the detection of infection was a radioimmunoassay based upon the first generated HCV protein (C100-3). This was soon put into an immunoassay format and in late 1989 it become available as the first generation immunoassay. Subsequently, the second– and third– generation ELISAs were developed by adding more epitope (C22, C33c, BHC7) to the solid phase of the test. Since the specificity of ELISA tests is limited especially in a low-risk population it, all positive ELISA results had to be confirmed. Several serological conformation tests (Western blot, immunoblot assay) using the same epitopes as the ELISAs have been developed. However, the antibody test cannot distinguish non-infectious individuals with resolvent HCV infections from infectious HCV–RNA carriers. Amplification of viral RNA sequences by the polymerase chain reaction (PCR) is the only practical method currently available for demonstrating viremia in patients with HCV infection. The purpose of this article is to present briefly the principles and some important technical details of all available diagnostic methods for the detection of HCV infection.