Tick-borne encephalitis (TBE) virus strains were isolated in West Siberia in the forest-steppe region near the Ob river in 1981-1992. Hybridization of genome RNA of 46 TBE strains with [32P]cDNA of TBE Sofyin strain revealed essential differences in the genomes of West-Siberian and Far-Eastern Sofyin strains of TBE virus. Nucleotide sequences of 6 TBE strains (1348-1503 n.) have been determined. A 89-98% homology of Siberian TBE strains has been shown, while the similarity of the respective fragment of E gene for West Siberian and Sofyin strains was no more than 81%. No significant changes in E gene of TBE strains have been detected over a 12-year period.