A new flavivirus, provisionally designated as hepatitis G virus, has recently been identified. Its genomic organization is similar to that of the hepatitis C virus (HCV) with which it has only 25% nucleotide homology. The virus is transmissible by blood transfusion, by exposure to blood products or by intravenous drug use. Concurrent infection with hepatitis B virus and HCV is common and persistent viraemia has been documented, in many cases in the absence of transaminase elevations.