Mycoplasma hyopneumoniae causes an economically significant respiratory disease of swine called Enzootic Pneumonia. The disease process is initiated by adherence of M. hyopneumoniae to the cilia of swine respiratory epithelium through an interaction involving P97, a surface-associated protein, and cilia-specific receptors. Binding specificity is associated with a repeat region located near the C-terminus of the P97 protein. Further analysis of the DNA sequences surrounding the P97 structural gene revealed an operon composed of two ORFs, P97 and one coding for a 102.3-kDa protein designated P102. Hybridization analysis and subcloning experiments showed that the P97 adhesin-encoding gene was present as a single copy in the M. hyopneumoniae chromosome. P102 sequences, however, were found on four distinct chromosomal fragments, suggesting that multiple copies of P102 were present in the chromosome. One of these clones was identified by screening the genomic library with swine convalescent sera showing that P102 is expressed in vivo during M. hyopneumoniae infections. All copies of P102 were mapped to a single chromosomal region comprising approximately 13% of the genome (140kb), although the exact distance between the copies is not known. The function of P102 is also not known, but the translated sequence shows a prominent transmembrane domain, suggesting that it may be a surface protein.