Six alphaviruses and four flaviviruses were inoculated intracerebrally into 1 to 3 days old suckling mice. All mice developed CNS diseases and died 2-5 days post-infection. It appeared that alphaviruses were more virulent than flaviviruses since they brought death to the injected mice earlier than the flaviviruses. The susceptibilities of nine different culture cells to those viruses were also investigated using plaque assay. BHK-21 cells produced clearer plaques and were more sensitive than other cells. Plaque reduction tests using antibodies against various viruses revealed no cross-reactions between alphavirus and flavivirus. However, minor cross-reactions were found within groups. The results of this study suggest that BHK-21 cells can be used for the large scale screening of viruses in domestic animal specimens and for detecting serum neutralizing antibodies against arboviruses.