Respiratory function was assessed at a median postnatal age of seven months in seven infants born prematurely who suffered from chronic lung disease and had a proven viral infection while on the neonatal unit (study group). The results were compared with those of seven infants with chronic lung disease who were gestational age- and gender-matched but who did not have a viral infection (controls). Six of the study group and two controls were symptomatic at follow-up. Airways resistance was significantly higher (p < 0.04) and specific conductance significantly lower (p < 0.05) in the study group compared with the controls. We conclude in premature infants with chronic lung disease that viral infections acquired in the neonatal nursery are associated with impaired lung function at follow-up.