Objective:A high prevalence of GB virus C (GBV-C)/hepatitis G virus (HGV) RNA and E2 antibodies is observable in human immunodeficiency virus type 1 (HIV-1)-infected individuals in Belgium, including intravenous drug users (IDUs), in whom the highest prevalence is observed. A molecular analysis of GBV-C/HGV could give indications on the origin of this infection in IDUs.Methods:We directly sequenced 7 GBV-C/HGV isolates from this IDU population and performed a phylogenetic analysis comparing the results to known GBV-C/HGV sequences.Methods:We directly sequenced 7 GBV-C/HGV isolates from this IDU population and performed a phylogenetic analysis comparing the results to known GBV-C/HGV sequences.Results:All 7 isolates were GBV-C/HGV genome type 2. Three were found to be subtype 2a, and 4 belonged to the 2b subtype. No specific clustering was observed for strains obtained from IDUs in Belgium, and they were interspersed between other sequences with long branch lengths.Conclusion:Based on our results, it is unlikely that the IDUs were infected recently by GBV-C/HGV from a common ancestral virus.Journal of Human Virology 1999;2:115-120 © Lippincott Williams & Wilkins, Inc.