Hypertonic saline challenge has become a standardized method for measuring airway responsiveness. However, there is still uncertainty about the occurrence of a late asthmatic response. Therefore, the present study was designed to assess a possible late asthmatic response after hypertonic saline challenge in children. Twenty-one children with mild to moderate bronchial hyperresponsiveness were studied. On days 1 and 2, forced expiratory volume in one second (FEV1) was measured hourly from 10:00 h to 22:00 h to assess diurnal variation of lung function. On the third study day, a hypertonic saline challenge was performed and FEV1 was measured as on control days. The possibility of a late asthmatic response was tested by comparing FEV1 levels up to 12 h after the challenge on the intervention day to FEV1 levels on control days. In no subjects were the FEV1 values following the challenge found to be considerably below the individual mean of the control days. Furthermore, a nonparametric approach was applied for each child and the population looked into as a whole. Again, no late asthmatic response was detectable. The results of this study suggest that in children with mild to moderate bronchial hyperresponsiveness a late asthmatic response does not occur 4-12 h after a 4.5% saline challenge.