ABSTRACT. We present five cases of soldiers admitted to hospital for community acquired pneumonia; seroconversion for Ehrlichia chaffeensis (E. chaffeensis) was detected in four and permanently elevated antibody titer in one of them. Ehrlichia is a microorganism which belongs to the Rickettsiae family and frequently causes disease in dogs transmitted via tick bite. The same route of transmission, although rare, applies also in humans and results in a systemic disease associated with haematological disorders and, in few cases, affecting the respiratory system as well. Doxycyclin is considered the treatment of choice. Most of the cases have been reported in the USA, but individual cases have also been reported in Europe. Diagnosis is based mainly on the detection of specific antibodies in serum and consistent clinical manifestations. In the cases we present, all patients had negative serology testing for viruses and atypical bacteria, but showed significant and rapid clinical improvement after administration of doxycyclin. Exposure to tick bites was considered highly probable due to military activities. Based on the clinical and laboratory findings, we considered E. chaffeensis or other relative species as a potentially responsible pathogen in these patients. To our knowledge no other cases of ehrlichiosis have been reported in Greece. Pneumon 2002, 15(1):63-73.