The aim of this study was to evaluate the associations between different pathogens in the development of pneumonia and bronchopneumonia in pigs. Samples of bronchoalveolar lavage fluid from 100 pigs showing no clinical signs and 239 pigs with clinical signs of respiratory disease were examined for Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, us-type porcine respiratory and reproductive syndrome virus (prrsv), eu-type prrsv, porcine circovirus type 2 (pcv-2), influenza virus type A, α-haemolytic Streptococcus species, β-haemolytic Streptococcus species, Pasteurella multocida, Bordetella bronchiseptica, Haemophilus parasuis and Actinobacillus pleuropneumoniae. These potential pathogens were detected more frequently in the pigs with respiratory problems than in the pigs with no clinical signs. pcv-2 and α-haemolytic streptococci were the pathogens most frequently detected; A pleuropneumoniae was isolated in only two cases. There were more often associations between the organisms in the pigs with clinical signs than in the healthy pigs. In particular, α-haemolytic streptococci and M hyopneumoniae were both associated with the presence of M hyorhinis, eu-type prrsv, P multocida and B bronchiseptica, and α-haemolytic streptococci also occurred more often in pigs that were already infected with other pathogens. P multocida and B bronchiseptica were both significantly associated with M hyopneumoniae, α-haemolytic streptococci, eu-type prrsv and us-type prrsv.