The laboratory methods available for the isolation and identification of Nairobi sheep disease virus have been compared. The results show that inoculation of tissue culture (BHK 21 C 13) with suspensions of infected organs or plasma followed by fluorescent antibody tests on coverslip preparations gave the quickest means of identification. This test did not depend on the production of a cytopathic effect. Primary isolation of the virus in infant mouse brain and identification either by fluorescent antibody methods or by complement fixation with antigen prepared from the mouse brain offers a slightly more sensitive isolation system and would be recommended where no tissue culture facility exists.