The invention relates to the identification of members of a gene family from the human respiratory pathogen Chlamydia pneumoniae, encoding surface exposed membrane proteins of a size of approximately 89-101 kDa, preferably about 89.6-100.3 kDa and about 56.1 kDa. The invention relates to the novel DNA sequences, the deduced amino acid sequences of the corresponding proteins and the use of the DNA sequences and the proteins in diagnosis of infections caused by C. pneumoniae, in pathology, in epidemiology, and as vaccine components.