The organ where the GB virus (GBV)-C/hepatitis G virus (HGV) localizes and proliferates is not known. We examined the digestive organs for HGV RNA to determine the localization of the HGV. Two cases of patients with serum-positive HGV RNA were investigated. We embedded surgically excised materials and digestive secretion materials from cases 1 and 2 in paraffin blocks. The tissue specimens investigated included lymph nodes No. 201 and 202, ascending colon (nontumor and tumor area), ileocecum, appendix, liver (nontumor and tumor area) and gall bladder. We made cDNA after extraction of total RNA from thin tissue sections and detected HGV RNA with a reverse transcription polymerase chain reaction method. No HGV RNA was detected in liver, colon and gall bladder tissues. HGV RNA was only detected in the appendix tissue. Comparison of nucleotide sequences of PCR products from serum and appendix was almost the same. Homology between US type (PNF2161) and the serum and appendix PCR products was 92.6 and 93.6%, respectively. These results suggest that HGV proliferates in the appendix and is carried by the portal blood flow to the liver, and may cause a hepatitis reaction in the liver.