The gene encoding antigenic site G(1) of bovine ephemeral fever virus (BEFV) was highly expressed in the host cell Escherichia coli. An indirect G(1)-ELISA with the recombinant protein as the coating antigen was established to detect antibodies against BEFV. The result revealed that the optimal concentration of the coated antigen was 0.5 microg/well and the dilution of serum was 1:20. It was optimal that sera with P/N >or= 2.2 were considered positive, P/N <or=2.0 negative, and between 2.0 and 2.2 ambiguous. The G(1)-ELISA method gave a sensitivity of 97.6% and a specificity of 98.6% by testing 590 field serum samples. These results suggest that the G(1)-ELISA may be a good alternative tool for seroepidemiological surveys.