A total of 500 sera and lungs of slaughtered pigs were examined to investigate antibody titer, prevalence of pulmonary lesion, and interrelation among lung lesion score, type of pulmonary lesion and antibody titers by ELISA. The results obtained were as follows ; 1. The highest distribution of antibody titer was showed at 20 - 80 in M hyopneumoniae, 160-640 in P multocida type A and 160 - 640 in A pleuropneumoniae serotype 2 and 5. 2. The prevalence of pulmonary lesions was 84.0%, mean pulmonary lesion and mean lung score listed as 24.0$pm$19.8% and 2.5$pm$1.6, respectively. 3. In the prevalence of type of pulmonary lesion, enzootic pneumonia, pleuropneumonia and pleuritis were 58.2%, 10.0% and 15.8%, respectively. 4. Lung lesion score and type of pulmonary lesion were not interrelated with the distribution of antibody titer to specific pathogens, and causative pathogens of respiratory diseases were complicated with various bacteria.