The aim of the study was to investigate the association between electromyography (EMG) of the diaphragm and intercostal muscles and the forced expiratory volume in 1 s (FEV(1)) at different levels of histamine-induced airflow limitation, and the response to salbutamol. Moreover, we assessed the reproducibility of the EMG measurements on 2 different occasions during different levels of airflow limitation in asthmatic school children. Fourteen children with asthma performed 2 histamine challenges with a 24-h time interval and 1 child performed 1 histamine challenge. The EMG signals were derived from surface electrodes. The logarithm of the EMG-activity-ratio (log EMGAR; mean peak-bottom ratio of respiratory muscle activity) was used as EMG parameter. The log EMGAR of the diaphragm (di) and the log EMGAR of the intercostal muscles (int) associated well with the histamine-induced fall in FEV(1) at 5% steps from the baseline value. After administration of salbutamol log EMGARdi and log EMGARint returned to baseline mean peak-bottom values (for all leads P<0.001). The EMGARdi and EMGARint values were reproducible at different levels of airflow limitation. This study showed that EMGARdi and EMGARint as a parameter for a change in electrical activity of the diaphragm and intercostal muscles associated well with FEV(1), was reversible after salbutamol and was reproducible at different levels of histamine-induced airflow limitation in asthmatic school children.