Analysis of low-molecular virus-specific proteins of all the known members of the tick-borne encephalitis (TBE) complex viruses: TBE (2 strains), Langat, louping-ill, Negishi, Kyasanur Forest disease, Omsk hemorrhagic fever (2 strains), and Powassan, was performed. The cells infected with the above viruses were found to contain low-molecular virus-specific NVX (with the exception of Powassan, Omsk hemorrhagic fever, and Kyasanur Forest disease viruses), NV21/2, NV2, NV11/2, and NV1 proteins. These proteins (except NV1) differ in the electrophoretic mobility in the viruses under study and in TBE strains No. 256 and Sophyin. Thus, electrophoresis may demonstrate differences in the characteristics of proteins of different TBE complex viruses and strains of one virus.