Abstract: Purified and isolated nucleic acid from specific strains of Haemophilus influenzae is provided which encodes at least a portion of the D15 outer membrane protein of Haemophilus. The nucleic acid is used to produce peptides, polypeptides and proteins free of contaminant associated with Haemophilus for purposes of diagnosis and medical treatment. Furthermore, the nucleic acid may be used in the diagnosis of Haemophilus infection. Antisera obtained following immunization with the nucleic acid D15 outer membrane protein or peptides also may be used for the purpose of diagnosis and medical treatment.