Treatment of tick-borne encephalitis (TBE) virus with Triton X-100 (TX-100), octylglucoside (OG) or cetyltrimethylammonium bromide (CTAB) caused dissociation of the virus envelope into dimers or monomers of the glycoprotein V3. By centrifugation into detergent-free sucrose density gradients, these subunits were found to reassociate and to form haemagglutinating homogeneous glycoprotein complexes sedimenting at 15 to 16, 16 to 18 and 11 to 23S after TX-100, OG and CTAB treatment, respectively. Glycoprotein complexes obtained after TX-100 solubilization contained less than 1% lipid and detergent by weight.