Chlamydophila pneumoniae is an obligate intracellular pathogens, that causes multiple types of respiratory tract infections.The exposure to this pathogen is quite common. C. pneumoniae may cause a persistent infection in multiple organs and may be associated with several chronic inflammatory conditions. The aim of this study is the evaluation of the serological epidemiology of C. pneumoniae infection in four heterogeneus groups of patients.The detection of antibodies anti-C. pneumoniae was conducted using an, in-house, microimmunofluorescence (MIF) test, as indirect diagnostic technique.