Subjects with asymptomatic airway hyperresponsiveness in epidemiologic studies may have variable airway obstruction that is not perceived as dyspnea. We tested the hypothesis that such subjects are less likely to report an increase in dyspnea during histamine-induced bronchoconstriction than symptomatic hyperresponders. A random population sample of 412 middle-aged subjects was studied. Before and after a standardized histamine challenge test, subjects recorded Borg scores for dyspnea: any increase in Borg score was considered significant. More than 80% of hyperresponsive subjects (PC10 histamine < or = 16 mg/ml) had no symptoms. The presence of prechallenge dyspnea was related to increased airways responsiveness and current smoking. An increase in Borg score was associated with younger age, more severe airway responsiveness, atopy, and female sex. The level of and increase in the Borg score were not significantly related to level and change in airway caliber (FEV1). In hyperresponsive subjects (PC10 < or = 16 mg/ml), subjects who reported dyspnea, wheeze, or asthma were more likely to show an increase in Borg score during histamine provocation than asymptomatic subjects (adjusted odds ratio 4.01, 95% confidence interval 1.01 to 16.00, p = 0.049), after adjustment for age, sex, smoking habits, FEV1, and atopy. This suggests that asymptomatic hyperresponders may have variable airway obstruction that is not recognized as breathlessness.