The airway response to nebulised ipratropium bromide was studied in 17 chronically or recurrently wheezy infants aged 4-15 months. The peripheral airway response was assessed by the change in maximum flow at functional residual capacity (Vmax FRC) and the upper and central airway response by the change in specific airways resistance. The significant reduction in specific airways resistance after treatment with ipratropium bromide signified an improvement in central and upper airway function. No change was found, however, in Vmax FRC and hence in peripheral airway function. It seems that, as in older subjects, inhaled antimuscarinic, anticholinergic drugs have their maximum effect on the large airways, and this may explain their lack of effect in the management of acute bronchiolitis.