Clinico-genetic analysis was performed in 530 patients with chronic bronchitis (CB) and in 760 healthy persons. The frequency of aggravated heredity in the patients' parents was significantly higher than that in the healthy persons' parents (21.3 +/- 1.8 and 12.1 +/- 1.2%, respectively, P less than 0.05), this predominance being associated with such diseases as chronic bronchitis and bronchial asthma. A study of a type of familial aggravation has shown that the probability of CB development in descendants increases substantially if mother suffers from CB, CB morbidity among girls being significantly higher than that among boys. The results of a sib analysis also confirm an important role of the genetic mechanisms in CB development. Investigations using a twin method (14 pairs of monozygotic and 39 pairs of dizygotic twins) have demonstrated that genetic factors account for 41% in the formation of the leading CB symptoms while exogenous factors account for 59%. A study of the blood antigens ABO, Rh, MN, P, Hp has revealed different sensitivity of persons with different genetic blood markers to CB. Differences in the frequency of antigen combinations were also revealed in the patients and in the healthy persons. The results obtained indicate the appropriateness of further development of genetic investigations in pulmonology.