Seventeen atopic (a positive skin-prick test result to at least one common aeroallergen) asthmatic patients were enrolled (mean [± SEM] FEV1, 76.9 ± 3.16% predicted at screening; mean age, 47 ± 3 years). All patients were receiving inhaled corticosteroids (mean, 570 μg/d of chlorofluorocarbon-propelled beclomethasone dipropionate equivalent), six patients were receiving long-acting β2-agonists, and two patients were receiving montelukast. All patients maintained their usual inhaled corticosteroid throughout the study; however, all long-acting β2-agonists and montelukast were stopped 48 h prior to the first challenge, and were withheld until after the second challenge; short-acting β2-agonists were withheld for 6 h prior to each challenge. All 17 patients attended the Asthma and Allergy Research Group, University of Dundee, for a full protocol AMP bronchial challenge from 0.09 to 800 mg/mL in almost doubling concentration steps, using the dosimetric technique described previously,9 to reach at least a 20% fall in FEV1. All concentrations of AMP were administered at constant 2-min intervals, with FEV1 measurements obtained 90 s after the final inhalation of each concentration of AMP. The highest concentration of AMP (Clinalfa; Merck Biosciences; Läufelfingen, Switzerland) administered to each patient was noted, along with the fall in FEV1 at this concentration. Patients then recovered spontaneously, with FEV1 measured at 2, 5, 10, 20, 30, 40, 50, and 60 min. Spirometry was carried out using a compact spirometer (Vitalograph; Vitalograph Ltd; Buckingham, UK) with a computer-assisted pneumotachograph head and pressure transducer. The spirometer was calibrated daily using a 1-L precision syringe (Vitalograph Ltd). The provocative concentration of AMP required to produce a 20% fall in FEV1 was calculated by linear interpolation of the log-dose scale. Patients returned to the department within 2 days, at which point they received only the highest concentration of AMP reached during the full protocol. The fall in FEV1 was noted, and spontaneous recovery of FEV1 was measured as before. Comparisons were made of the fall in FEV1 and the time to spontaneous recovery, defined as time for FEV1 to return to within 5% of baseline. Statistical comparisons were made by means of paired t test. This study received ethical approval from the Tayside Committee on Medical Research Ethics on November 13, 2003 (reference 201/02).