In a group of 1,958 screened subjects the FEV1, FVC and FEV% were used to define three sub-groups – normal, borderline and abnormal based on prediction formulae derived from two different normal populations. Using other criteria of respiratory disease the borderline and abnormal groups differed significantly from normal. Smoking was an important feature which distinguished subjects with borderline impairment from the rest. More females than expected had ventilatory dysfunction, an increase which was not accompanied by a proportional increase in symptoms attributable to chronic bronchitis