During the last 15 years, several new bacterial species related to Chlamydia have been discovered within amoebae. Their ability to grow within these professionnal phagocytes suggests that they are also resistant to destruction by other phagocytic cells such as alveolar macrophages and that they may be excellent candidates as new agents of pneumonia. There are growing evidence that these Chlamydia-like organisms play a role as etiological agent of lower respiratory tract infections. Thus, Parachlamydia is apparently an agent of inhalation pneumonia and--at least in the immunocompromised host--of community-acquired pneumonia, whereas Simkania is considered as a common agent of bronchiolitis and an emerging agent of pneumonia. Nevertheless, their pathogenic potential remains underestimated since these obligate intracellular bacteria grow only poorly or not at all on the culture media generally used to detect pathogen in diagnostic laboratories.