The aim of the study was to assess the degree of airways involvement in non-smoking subjects with extrinsic allergic alveolitis resulting from pigeon-derived antigens. Two hundred and eight pigeon fanciers completed a questionnaire of symptoms, performed spirometry on a Vitalograph Compact spirometer and had IgG antibody to pigeon gamma-globulin measured. Eighty fanciers had the acute form of pigeon fanciers' lung (PFL) and these subjects were less likely to be current smokers (P less than 0.001). Subjects with PFL had a higher prevalence of chronic bronchitis (P less than 0.001), large airways (P = 0.014) and peripheral airways obstruction (P less than 0.001). The prevalence of chronic bronchitis and peripheral airways obstruction increased significantly as the level of antibody to pigeon gamma-globulin rose. Peripheral airways obstruction, as manifest by a reduced FEF25-75%, was the most common abnormality found. Airways disease is an important feature of the acute form of PFL and consists of a hypersecretory disorder in the form of chronic bronchitis and of obstructive airways disease particularly affecting the peripheral airways.