Over a period of six months, approximately 4700 blood samples were collected from 97 pig‐finishing farms in the provinces of Noord‐Brabant and Gelderland and screened for antibodies with respect to Aujeszky's disease virus (ADV), porcine influenza virus (PI) andActinobacillus(Haemophilus)pleuropneumoniae(App). There were significant differences in the percentages of seropositive pigs between the two provinces, which may be related to the difference in the density of the pig population in the two provinces.