The genes encoding homologous 85 kDa outer membrane proteins of Neisseria gonorrhoeae and Neisseria meningitidis have been cloned and sequenced. The gonococcal gene, omp85, was identified by screening a genomic library with an antiserum raised against purified gonococcal outer membranes. The gene encoded a 792 amino acid protein, Omp85, having a typical signal peptide and a carboxyl-terminal phenylalanine characteristic of outer membrane proteins. The amino acid sequence was similar to that of the D15 protective surface antigen (D-15-Ag) of Haemophilus influenzae, and the Oma87 of Pasteurella multocida. Southern analysis demonstrated that omp85 was present as a single copy in N. gonorrhoeae and N. meningitidis. PCR amplification was used to obtain a clone of the N. meningitidis omp85 homologue. Sequence analysis revealed that the N. meningitidis Omp85 was 95% identical to the N. gonorrhoeae Omp85.