We reported that HCV particles were 55 to 65nm spherical particles with fine surface spike-like projections by immunoelectron microscopic study using anti-HCV E1 antibodies in 1994. In this study, we tried to determine the distribution of HCV E2/NS1 antigen on HCV particles.(MATERIALS and METHODS) HCV particles (subtype 1b, > 10 9 copies/ml) in the sucrose density gradient fractions were examined the reactivity with polyclonal and monoclonal antibodies to HCV E2/NS1 glycoprotein by indirect immunogold electron microscopy. A double staining of HCV E1 and E2/NS1 antigens on HCV particles was also done.(RESULTS) HCV particles were specifically reacted with anti-E2/NS1 antibodies and these were doubly stained by specific gold labelings of anti-E1 and anti-E2/NS1 antibodies.(CONCLUSION) HCV E1 and E2/NS1 antigens were simultaneously distributed on the surface of the virion.