A random sample of subjects over 65 years of age who had replied to a postal questionnaire on respiratory symptoms was asked to attend for lung function studies and, if fit, an inhaled methacholine bronchial challenge. Of 283 subjects, 180 (63.6%) agreed to attend. Most (98%) subjects performed reproducible spirometry, with no evidence of fatigue on repeated testing. However, 20 subjects were found to be unsuitable for challenge (forced expiratory volume in 1 s, (FEV1) < 1 litre or unable to perform spirometry reproducibly). The dose of methacholine producing a 20% fall in FEV1 was termed the PD20. A positive challenge with PD20 < 6.13 μmol methacholine was found in 69 of 160 (43%) subjects studied, with highly reactive airways (PD20 < 1.0 μmol methacholine) in 19 of 160 (12%). Bronchial hyperreactivity, which is closely associated with clinical asthma, was found to be far more common amongst the elderly than previously recognised. Low initial FEV1 (1-1.5 litres) predisposed to both a positive challenge (p < 0.01) and also to highly reactive airways (p < 0.01), generally associated with respiratory symptoms. Subjects with low (1-1.5 litres) baseline FEV1 were five times more likely to have highly reactive airways than those with FEV1 1.5 litres, confirming a relationship between baseline airway calibre and bronchial reactivity. Early detection of subjects with low FEV1, who are therefore more likely to have increased airway reactivity, may help to reduce respiratory morbidity in the elderly with considerable benefit both to patients and to the Health Servic