Samples of sera from broiler chicken and broiler chicken breeder flocks of North Western Germany were examined for presence of antibodies against Ornithobacterium (O.) rhinotracheale with a self-developed ELISA system. A total of 3600 samples of sera from 190 broiler flocks in 70 different farms were tested. In 332 samples of sera (9.4%) from 25 flocks (13.2%) in 22 farms specific antibodies were detected. Additionally, serum samples from the breeder hens, taken between the 9, and 61, weeks of age were tested. In 28 from 29 flocks (96.6%) specific antibodies were detected using this ELISA-system. First detectable antibodies were found between the 14, and 36, week of age in the parent breeder flocks. These results show that infections with O. rhinotracheale are widely distributed in the parent-breeder chicken broiler flocks. The significance of this bacterium as the cause of respiratory diseases in chickens are discussed.