Forty, 8-week-old, Large White Landrace pigs from a unit of a high health industrial pig farm, which was frequently monitored for A. pleuropneumoniae, were used. No clinical signs or A. pleuropneumoniae-associated lesions have been reported in the selected farm during the past five years. In addition, the exposure of the animals to A. pleuropneumoniae was ruled out by means of microbiolog- ical isolation from nasal swabs during the acclimatization period and by a commercially available ELISA kit (IDEXX APP-ApxIV Ab Test, IDEXX, Maine, USA).