AbstractHepatitis C virus (HCV) infection is etiologically associated with the development of hepatocellular carcinoma (HCC) worldwide. HCV has been reported to exist and replicate in both HCC and adjacent non‐cancerous liver tissue, but limited information was available on HCV viral load and quasispecies composition in HCC relative to adjacent non‐cancerous hepatocytes. Previous study has also suggested CD81, a surface hepatocyte protein, as a receptor for HCV. To clarify the above, HCV‐RNA and CD81‐RNA titers in 20 paired hepatectomized liver and serum were quantitatively measured by chemiluminescent RT‐cPCR. Hypervariable region 1 (HVR‐1) variations of parallel specimens were analyzed after subcloning in 6 patients. HCV‐RNA levels in serum and non‐cancerous liver were markedly higher for HCV genotype 1 than genotype non‐1. HCV levels were markedly higher in non‐cancerous liver than in HCC (P = 0.001) in a genotype‐independent manner, with a mean ratio of 56:1 for non‐cancerous tissue to HCC. Both non‐cancerous and HCC tissues had the same level of CD81‐RNA expression, which was not linked to HCV load. HCV‐RNA quantity in both HCC and non‐cancerous liver correlated with the number of HVR‐1 quasispecies in the tissue, and distinct HVR‐1 subclones existed. J. Med. Virol. 68:188–196, 2002. © 2002 Wiley‐Liss, Inc.