Hyper immune sera were prepared in rabbits and cattle against rabies and bovine ephemeral fever (BEF) viruses with the conjugation of some portions of them with FITC. Neutralizing antibodies were estimated in each serum and it was found that rabies antibody titers were higher in rabbits than in cattle while those of BEF were higher in cattle than in rabbits. Homologous and heterologous application of SNT, AGPT and direct fat revealed that the homologous tests resulted in higher titers and more clear reactions than in hetreogenous tests indicating that there is a little antigenic relationship between rabies and BEF viruses. This relation may be used in the diagnosis of any of the two diseases in the absence of its specific antiserum but with taking in consideration the case history of animal biting and history outbreaks of BEF in addition to clinical symptoms.