Introduction: Polymorphonuclear neutrophil leukocytes ( PMNL) have an important defensive role against various microorganisms and other agents,but by liberating various substances, first of all the superoxide anion (O 2Ë‰), they can damage the bronchial mucosa and influence the development of bronchial inflammation which is the fundamental of bronchial hyperreactivity (BHR). Objective: to show the role of the PMNL for development and level of BHR in patients with chronic obstructive pulmonary disease ( COPD). Material and methods: We observed 160 patients with COPD treated in Clinic for Pulmonary Diseases and TB “Podhrastovi” Sarajevo during three years :from 2012 to 2014. They were divided into groups and subgroups according to the first registration of BHR in the course of illness and to the number of exacerbations of the disease in one year. The number of blood PMNL was measured in a stable state of disease at the begging and at the end of investigation. Results: The number of blood PMNL was significantly greater in patients with 3 or more exacerbations per one year ( p
polymorphonuclear neutrophil leukocytes, BHR, COPD.