Dose-response curves were established in asthmatics by using graded doses of aerosolized carbachol and specific airway conductance (SGaw) measurements. After carbachol inhalation, we evaluated the influence on SGaw of a deep inspiration to total lung capacity followed by a passive expiration to functional residual capacity. When SGaw had returned to its pre-deep-inspiration value, forced expiratory volume in one second (FEV1) was obtained. Two groups of patients were selected according to the effect of deep inspiration on SGaw: group A (22 patients) with a less than 25% SGaw increase after deep inspiration, and group B (21 patients) with a more than 75% SGaw increase. Both groups were comparable in age and initial SGaw and FEV1 values. Carbachol inhalation induced a similar SGaw decrease in both groups, whereas FEV1 decreased more (p less than 0.05) in group A than in group B. The two groups did not differ significantly regarding the dose of carbachol causing a 25% SGaw decrease and in the slope of the dose-response curve. We conclude that, in asthmatic patients, airway response to an inhaled broncho-constrictor agent is not related to the airway response to deep inspiration. This suggests that previous studies of airway response to bronchoconstrictor agents which have been performed by using only FEV1 measurements, may need to be reassessed.