A virus strain was isolated fromVespertilio pipistrellus Schreber, 1775 while examining bats in Sokuluksk region of the Kirghiz S.S.R. in 1970. Hemagglutination inhibition tests indicated that the virus ranged among group B arboviruses. It differed essentially in complement fixation and neutralization tests from 30 viruses of the B group: Entebbe bat; Bukalasa bat; Dakar bat; Kadam; Modoc; Spondweni; Ilheus; Japanese, St. Louis, Murray Vallay and tick-borne encephalitis; Kyasanur Forest disease; Powassan; Langat; Tyuleniy; West Nile; Bussuquara; Cowbone Ridge, Uganda S; SAH-336; Kokobera; yellow fever; Dengue, types 1 and 2; Wesselsbron; Edge Hill; Alfuy; Stratford; Zika; Potuskum. It may be concluded that Sokuluk virus is a new group B virus. Complement-fixing antibodies were not found in sera of 150 cows and 200 sheep but they were detected in 0.6 percent of 579 human sera in the Kirghiz S.S.R.