The 'long PCR' was used for amplification of hepatitis C virus (HCV) subgenomic fragments from liver. After testing several commercially available systems, it was found that Tth as the major enzyme is superior to using Taq. Employing a mixture of Tth and Vent polymerase (rTth polymerase, XL, Perkin Elmer) it was possible to amplify 4.6-kb and 9-kb fragments from biological samples containing as little as 10(2) and 10(4) viral copies, respectively. It was also demonstrated that 'long PCR' is useful for joining together large size amplification products.