By means of overlapping peptides expressed in Escherichia coli in combination with Western-blotting, infection specific linear epitopes were identified on the non-structural protein 3ABC of FMDV. The epitopes reacted with sera from pigs or guinea pigs infected with different serotypes of FMDV, but not with sera from normal or vaccinated animals. A protein was constructed by tandem repeat of the epitope covering amino acid residues 141-190 on 3ABC. An ELISA based on the protein with tandem epitopes could be used as a diagnostic antigen for differentiating infected pigs from vaccinated ones.