The cytologic and immunologic analysis of bronchoalveolar washing offs and of peripheral blood was made in 45 patients with chronic bronchitis. Of these, 27 patients suffered from catarrhal bronchitis without infection signs and 18 were affected with purulent bronchitis with superinfection. It has been shown that discovery of a considerable number of neutrophils in the bronchoalveolar washing offs promotes the establishment of the infectious etiology of chronic bronchitis. The immunologic analysis of the washing offs was found to be of great informative value in the study of the mechanism of the disease development. Pronounced dysfunction of the immune system and its manifestations common to catarrhal and purulent bronchitis were demonstrated. It is concluded that dystrophic processes predominate in the lungs of the patients with chronic purulent bronchitis whereas catarrhal bronchitis is marked by the high local immune reactivity in the lungs. The characteristic features revealed are regarded as criteria of the differential diagnosis between the given bronchitis patterns. It has been disclosed that impairment of the mechanisms of cellular immunity is one of the properties shared by both the disease patterns. The authors discuss the prospects of the use of the combined immunologic analysis of the bronchoalveolar washing offs and peripheral blood in patients with chronic bronchitis.