The content of products of lipid peroxidation and antioxidative activity were measured in exhaled air condensate and blood sera of patients with chronic bronchitis. Exacerbation of purulent bronchitis was found to be associated with an increase of heptane-soluble products of lipid peroxidation in serum and condensate, which was not observed in patients with catarrhal bronchitis. In catarrhal bronchitis, the content of heptane-soluble products is increased only in the serum; antioxidative activity increased in exhaled air condensate in catarrhal bronchitis and decreased in serum and condensate in purulent bronchitis.