Recurrent respiratory symptoms are common in preterm infants in the first 2 years of life. The aim of this study was to determine the lung function abnormalities associated with such symptoms. Forty preterm infants, with a median gestational age of 29 weeks were studied at a median postnatal age of 12 months. Twenty-two suffered from recurrent symptoms, defined as wheezing and/or coughing on at least 4 days per week over the previous month. Lung function was assessed by measurement of functional residual capacity (FRC), using a helium gas dilution technique, and airway resistance (Raw) and thoracic gas volume (TGV) plethysmographically. No significant difference was found in TGV between symptomatic and asymptomatic infants, but the median FRC was lower (P less than 0.01), Raw higher (P less than 0.01), and FRC:TGV ratio lower (P less than 0.001) in the symptomatic infants. These lung function abnormalities in the symptomatic infants are suggestive of gas trapping.