The antigenic components of eight serotypes of Haemophilus pleuropneumoniae (HP) were analyzed by sodium dodecyl sulfate polyacrylamide gel electroghoresis (SOS-PAGE) and Western imm-unobJotting technique. There were about 38 bands and more than 45 bands of each type revealed in SOS-PAGE with Coomassie blue and silver stain, respectively. However, there was no significant difference among serotypes. The compositions of difference ser-otypes of HP were very similar. In Western blotting, there were 30, 15 and 13 antigenic bands of each strain, respectively, when the blotting profile reacted with antisera against whole ceUs, serum from pig naturally exposed to HP and serum against pur-ified lipopolysaccharides (LPS). From the patterns obtained in Western blots, it was suggested that the surface antigens played a major role in provoking immune response. There were two add-itional antigenic bands, 43K and 70K of serotype showed in Western blots, reacting with antisera against serotype 1. They were concluded to be serotype-specific.