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Classical swine fever (CSF) is an endemic disease in many countries. A key tool for laboratory confirmation of CSF is a differential diagnosis between vaccinated and actually infected pigs. Many enzyme-linked immunosorbent assays (ELISA) are based on the capture of antibodies in animal sera, but these tests cannot be used in animals that are persistently infected. In these cases, an antigen-capture ELISA may be a good choice to differentiate vaccinated animals from those that are infected. In order to produce a polyclonal antibody that allows this technique, two rabbits were immunized with recombinant Erns protein. The antibody was conjugated to horseradish peroxidase (HRP) and the optimal working dilution was 1:64 000 in a direct ELISA. Different coating conditions were evaluated to trap recombinant Erns in a sandwich ELISA and it was concluded that coating at 10 µg/mL would ensure greater capture. The ELISA was able to detect Erns from a mixture of sera from pigs vaccinated with the Chinese strain of classical swine fever virus (CSFV). In addition, no reaction was observed in sera from healthy animals or in sera from animals vaccinated with Porvac®, an E2 protein subunit vaccine. It was concluded that the generated polyclonal antibody can recognize the viral Erns protein in pig sera, so it could be used in a sandwich ELISA to differentiate healthy animals from those infected with CSFV. [ABSTRACT FROM AUTHOR]