The gene for outer membrane protein P5 of Haemophilus influenzae was identified by immunological screening of a genomic lambda EMBL3 library of the serotype b strain 1613. The gene was subcloned, and plasmid clones expressing P5 were identified by immunologic screening. The gene for outer membrane protein P5 was sequenced. The mature protein has a molecular weight of 35,628. The protein is 50% identical and 65% similar to the OmpA protein of Escherichia coli.