In epidemiological studies, defining asthma as the presence of airway hyperresponsiveness (AHR) plus recent symptoms leaves two groups of subjects whose clinical significance is unclear: those with asymptomatic AHR, and those with symptoms only. The aim of the study was to determine whether subjects with symptoms only differ from the normal and asthmatic groups in the perception of airway obstruction. Six hundred and ninety seven adults completed a questionnaire of symptoms and underwent bronchial challenge with histamine to induce airway obstruction. Recent symptoms included wheeze and morning chest tightness in the last 12 months. AHR was defined as a provoking dose of histamine causing > or = 20% fall in forced expiratory volume in one second (PD20FEV1) <3.9 micromol. At the end of the challenge test, subjects who felt wheezy or tight in the chest marked a value from 0 to 10 on a modified Borg scale, to describe the severity of the sensation. Subjects with asymptomatic AHR did not differ significantly from subjects with AHR plus recent symptoms (current asthma) either in the mean fall in FEV1 or in the median Borg score. In subjects with symptoms only, the mean Borg score was not significantly different from that of the asthmatic subjects, although mean fall in FEV1 differed significantly (p<0.0001). In subjects with symptoms only, chest tightness correlated significantly with the fall in forced vital capacity (FVC) (p= 0.011), but not with the fall in FEV1. Subjects with asymptomatic airways hyperresponsiveness were not poor perceivers of airway narrowing, but may underreport their symptoms. Subjects with symptoms only may have enhanced perception of small changes in lung function, particularly in forced vital capacity.