Mycoplasma hyopneumoniae polypeptides and nucleic acids, as well as nucleic acid expression vectors and host cells containing nucleic acid vectors are provided. In addition, compositions containing M. hyopneumoniae polypeptides and nucleic acids are provided for use in methods of treating swine to prevent enzootic pneumonia. Furthermore, the invention provides diagnostic tests for the detecting of M. hyopneumoniae infection in swine herds.