The aim of this study was to specify whether during exercise the neural response to increased resistive load in asthmatic children corresponds to a modification of the neuromuscular inspiratory drive, to a modification of the breathing pattern, or to both. Thus, nine children with mild or moderate asthma (aged 10-15 yr) and nine normal children (aged 11-16 yr) were studied during an incremental load exercise with a cyclic ergometer, the load of which was increased by steps of 30 W.3 min-1. During the 3rd min of each workload, we measured the following parameters: O2 consumption (VO2), CO2 production (VCO2), ventilation (VE), tidal volume (VT), respiratory frequency (f), ratio of inspiratory to total time of respiratory cycle (T1/TTOT), mean inspiratory flow (VT/T1) as well as mouth occlusion pressure measured at 100 ms (P0.1), and inspiratory power for breathing (W). At maximum level, the two groups showed identical values for heart rate, ventilation divided by weight (VEBW), T1/TTOT), VT/T1, P0.1, and W. However, asthmatic children had lower maximal power (P less than 0.02), higher tidal volume divided by weight (VTBW) (P less than 0.05), and lower f (P less than 0.01). At a same level of exercise (60, 90, or 120 W), in both groups, we found identical values for P0.1, VEBW, VO2, T1/TTOT, and VTBW/T1. However, asthmatic patients exhibited higher VTBW and lower f(limit of significance). This resulted from higher inspiratory and total time durations. Furthermore, they showed a higher inspiratory power for breathing. It was the same for f and VTBW if the results were expressed in relation to the VO2 in ml.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)