The relationship between pertussis infection and subsequent abnormalities of pulmonary function is not clear. Thirty subjects (16 male, 14 female) aged 14.3 years (s.e.m. = 1.9) were studied who had been hospitalized with culture-proven pertussis when less than 6 months of age. Details of respiratory symptoms in the subjects and their families were obtained. Standard spirometry, lung volumes by body plethysmography, maximum flows at low lung volumes and histamine challenges were performed. Nine of 30 (30%) subjects were symptomatic with a history of recurrent cough and wheeze while 11 of 30 (37%) had abnormal pulmonary function tests. Seven of nine symptomatic subjects had abnormal pulmonary function including positive histamine challenges. Twenty-one per cent had a family history of asthma. This study indicates that children hospitalized in infancy with pertussis can subsequently be shown to have recurrent lower airways symptomatology and abnormal pulmonary function, but the incidence is not significantly higher than a control group from the same socio-economic background.