Airway reactivity and disease severity were investigated in 24 subjects with stable chronic bronchial asthma. Disease severity was determined by assigning a disease severity score (DSS) representing six clinical and therapeutic parameters. Airway hyperresponsiveness was assessed in two ways: airway reactivity score (ARS) based on the number of positive responses to a question concerning exposure to 22 nonspecific inhaled irritants and methacholine challenge testing and determining the cumulative dose causing a 20% reduction in FEV2 (CMD20). A significant correlation between DDS and CMD20 (r = 0.57; p less than 0.003) and DSS and ARS (r = 0.67; p less than 0.0003) attested to the important influence of airway hyperresponsiveness on disease severity. Significant correlations for ARS with CMD20 (r = -0.60; p less than 0.002) suggested the consistency with which the ARS estimated methacholine hyperresponsiveness. We found no statistically significant correlations between DSS, ARS, or CMD20 and the age of subject, duration of asthma, or other host characteristics. There was not a significant correlation between the degree of airway obstruction and DSS or ARS noted. The results of this investigation demonstrate the value of the use of clinical information for assessing airway hyperresponsiveness and disease severity in patients with chronic stable asthma. Both ARS and DSS are useful clinical tools for estimating methacholine reactivity.