Possible relations between nasal airway dimensions and measures of lung function are not well established. It has been suggested that a major part of airway resistance is found in the nose. However, little is known about the shape of tidal flow volume (TFV) loops in relation to nasal caliber. We therefore investigated whether lung function assessed by tidal breathing in healthy newborn infants was affected by nasal airway dimensions. Nasal airway dimensions were measured in 17 healthy newborn babies (mean age, 2.7 days) by acoustic rhinometry before and immediately after lung function measurements. Lung function was evaluated by TFV loops and passive respiratory mechanics (single-breath occlusion technique), first with both nostrils open, and subsequently immediately after occlusion of the larger of the two nostrils, causing at least a 50% reduction in nasal minimum cross-sectional area (MCA). Neither the TFV expiratory ratios (time and volume to reach peak flow to total time and volume, respectively [t(PTEF)/t(E) and V(PTEF)/V(E), respectively]), nor resistance or compliance of the total respiratory system differed significantly regardless of whether one or both nostrils were open. With one nostril closed there were no significant effects on any of the measured lung function parameters. We conclude that in healthy awake neonates reducing the cross-sectional area of nasal dimensions by 50% does not affect TFV loops or passive respiratory mechanics.