To determine whether inhaled budesonide given after allergen inhalation challenge inhibits the late asthmatic response (LAR) and/or the associated increase of airway responsiveness to methacholine, we performed a double-blind randomized cross-over study in 12 adult asthmatics (eight male, four female; mean age, 20.3 yr; range, 18 to 29 yr) sensitized to Dermatophagoides pteronyssinus (DP) previously shown to develop early and late asthmatic response to allergen challenge with DP. On different days each subject was randomized to receive budesonide 800 micrograms by Turbuhaler or placebo, given three times; (1) after allergen inhalation, after the onset of LAR, when FEV1 had fallen by > or = 15%; (2) 2 h later; (3) 4 h later. Airway responsiveness to methacholine was measured before allergen challenge at 8 to 10 h from allergen inhalation and 24 h after the allergen inhalation. Inhaled budesonide significantly reduced the LAR induced by allergen (maximal % fall in FEV1, delta FEV1%: -23 +/- 6% with budesonide versus -38 +/- 9% with placebo; p < 0.001) and inhibited the associated increase of airway responsiveness (geometric mean of PD20FEV1 methacholine: 0.047 mg after budesonide versus 0.033 mg after placebo at 8 to 10 h, p < 0.05; 0.119 mg after budesonide versus 0.062 mg after placebo at 24 h, p < 0.01). These results suggest that inhaled budesonide may not only prevent but also reduce the late asthmatic response induced by allergen and that it might also be considered in the treatment of exacerbation of asthma.