A new hepatitis G virus was identified by two independent research groups in 1995. To identify the new virus, molecular cloning was initially used. The viruses have been termed GBV-C hepatitis virus and hepatitis G virus (HGV). Since the complete sequences are now available in the Genebank database, it is obvious that they are two strains of the same virus. GBV-C/HGV is a single-stranded RNA virus, belonging to the family Flaviviridae, similar to the hepatitis C virus (HCV) as to the genomic organization. It can be transmitted by blood transfusion. There are several risk groups for HGV infection, such as multiply transfused patients, haemodialysis patients, recepi- ents of blood products, intravenous drug users. Many methods for HGV RNA detection exist using high conserved regions of HGV genome (5’-untranslated region and NS5a region). However, interlaboratory quality control programmes revealed poor standardization and significant differences mainly in sensitivity of molecular biological methods. These results suggest that laboratories willing to use the polymerase chain reaction (PCR) for detection of GBV-C/HGV RNA for research or diagnostic purposes should participate in multicentre quality control trials. The present work deals also with the clinical significance of HGV infection. Examples of prevalence of HGV RNA in certain groups are also noted. Recent clinical studies show the small significance of HGV infection in the etiology of non-A–E hepatitis, cryptogenic liver disease, hepatocellular carcinoma or in proceeding HCV coinfection. Despite this, it is not known whether HGV can be associated with other diseases in humans, is an orphan virus, or only becomes virulent under certain conditions.

        Key words: HGV, GBV-C, hepatitis G virus, HGV RNA, RT-PCR, non-A–E hepatitis, liver disease, HGV infection.