Airway reactivity is known to increase in relation to the severity of asthma, and, in the community, hyperreactivity has been shown to be associated with respiratory symptoms such as wheezing and shortness of breath. However, the relation between change in airway reactivity and change in the severity of respiratory symptoms and change in the use of asthma medications within subjects has not been studied. We have investigated this relationship in a community population. In September 1984 and March 1985, the provocative dose of histamine producing a 20% fall in FEV1 (PD20) was measured, and respiratory symptoms and medication use assessed by questionnaire in 78 subjects taking part in a study of seasonal changes in airway reactivity. On both occasions, PD20 was negatively correlated with current frequency of wheezing, with the amount of asthma medication in regular use, and with the current general assessment of breathing problems. In the 45 subjects who had a PD20 value of 8 mumol or less on at least one of the two occasions tested, PD20 increased between September and March by 0.46 (SEM, 0.32) doubling doses of histamine (p = 0.16). Within subjects, change in PD20 was negatively correlated with change in the frequency of wheezing in the past month (p less than 0.005) and with change in medication use (p less than 0.05). This study demonstrates that PD20 is related to the severity of respiratory symptoms and medication use, and that change in airway reactivity within subjects in a community population is associated with changes in the frequency of wheezing and in the use of asthma medication.