A genomic library of Mycoplasma pneumoniae was constructed by cloning sheared genomic DNA into the expression vector lambda gt11. Recombinant clones were screened using anti-M. pneumoniae mAbs reactive with adhesin P1 epitopes that mediate cytadherence. 10 clones with different size inserts were isolated. These clones possessed P1 sequences localized to the COOH terminus of the P1 gene. All clones produced fusion proteins that reacted with acute and convalescent sera of patients infected with M. pneumoniae. Interestingly, one clone, P1-7, contained an epitope that was confined to a region of 13 amino acids present in the M. pneumoniae genome as a single copy. The identification of this cytadherence-related epitope permits the production of a synthetic peptide that can be used as a rational vaccine candidate and serodiagnostic probe.