Four methods used for the detection of antibodies to Aujeszky's disease virus in porcine sera were compared. The serum neutralisation test, countercurrent immunoelectrophoresis test, micro-immunodiffusion test and the enzyme-linked immunosorbent assay (Elisa) were assessed with particular regard to their use in large scale screening of porcine serum samples. The Elisa test was found to be the most suitable on the grounds of sensitivity, speed and cost.