Анотация: Pneumonia in children is very common and of great social relevance. Despite the big advance in prophylaxis, diagnostic methods and the development of new antibiotics, there is no significant decrease in morbidity and mortality, and the incidence of recurrent and protracted pulmonary infections is rising. Mycoplasma pneumoniaе and Chlamydia pneumoniaе are the likely etiological causing agents in persisting pneumonia in children. Non-specific clinical, laboratory and x-ray findings in cases related to these agents are discussed, laying particular stress on the serological diagnosis and its interpretation