Hyperventilation of cold dry air causes bronchoconstriction in asthmatic subjects and has been proposed as a test for assessing bronchial hyperresponsiveness. The influence of the duration of inhalation of unconditioned cold air has not been studied. We have investigated the question in 12 asthmatic subjects in a clinically stable state. Each subject underwent three inhalation tests at a maximum interval of two weeks. On each day, the duration of inhalation was different, being randomly 2, 3 or 4 min depending on the subject. Doubling doses of cold air produced by a freon conditioner were administered, increasing ventilation from 7.5 to 15, 30, 60 l.min-1 and maximum voluntary ventilation (MVV). Forced expiratory volume in one second (FEV1) was assessed after each period of cold air inhalation. The test was stopped when the FEV1 had decreased by 20% or more, or when MVV had been achieved. The dose of cold air expressed as the level of ventilation causing a 20% change in FEV1 (PD20) was interpolated from individual dose-response curves. Dose-response curves shifted to the left when the duration of ventilation was increased. PD20 was significantly lower after 3 min of ventilation than after 2 min (mean +/- SD PD20 of 41.7 +/- 1.4 l.min-1 compared with 53.3 +/- 1.2 l.min-1; p = 0.002). There was a further fall in PD20 after 4 min of ventilation (PD20 = 36.1 +/- 1.5 l.min-1) but the difference compared with the values obtained after 3 min was not significant (p = 0.09), thus suggesting a plateau.(ABSTRACT TRUNCATED AT 250 WORDS)