Bronchial hyperresponsiveness is widely recognized as a marker of airway inflammation in asthma. The degree of bronchial hyperresponsiveness following acute severe attacks of asthma and the time course of its recovery has not previously been studied. Bronchial responsiveness to histamine was measured in 18 unselected patients admitted to hospital because of acute severe asthma, during their acute admission, and geometric mean PD₂₀ histamine was 0·08 (range 0·02–0·32) μmol. In nine patients, further measurements were performed at 3–4 and 12 weeks following discharge. Geometric mean PD₂₀ histamine was 0·09 μmol acutely, 0·23 μmol at 3–4 weeks (n=9, P=0·05 by analysis of variance) and 0·59 μmol at 12 weeks (n=8, P=0·04). For the eight patients studied at 12 weeks, a mean 10·3-fold increase in PD₂₀ was shown, with no suggestion of a maximum effect having been achieved. In contrast, spirometry had returned to the normal range by 4 weeks. The dissociation between improvement in bronchial hyperresponsiveness and spirometry is of interest. The delayed reduction in hyperresponsiveness may have important clinical implications for the duration of anti-inflammatory corticosteroid treatment following acute severe asthma.