The flow-volume profile of a maximum voluntary cough resembles that of a maximum expiratory flow-volume (MEFV) curve with superimposed transient peak flows at the onset of each cough effort and portions of zero flow corresponding to periods of glottis closure. A straight line (the cough slope) can be drawn through the transient peak flows, and the ratio of MEFV-equivalent flow to the cough peak flow can be calculated. This cough ratio has been shown to fall during adult life and may be related to changes in airway compliance and cross-sectional area with age. The present study investigated the cough ratio, cough slope, and maximum flows measured from the cough flow-volume curve in a group of normal children aged 7 to 16 years. Maximum flows and the cough slope increased with height, but the cough ratio did not change with growth or age. In a similar group of asthmatic children, baseline measurements of cough showed a reduction in cough peak flow rates, MEFV-equivalent flow, and the cough ratio. These changes are related to alterations in airway compliance and cross-sectional area and are partly reversed following inhalation of a bronchodilator.