Abstract Inhaled β-agonists can produce bronchodilatation and reduce airway hyperreactivity in patients with asthma. Using these two measures, we compared inhaled bitolterol (three puffs, 1110 μg), albuterol (two puffs, 180 μg), and placebo administered by metered-dose inhaler in a blinded, crossover study of 40 subjects with chronic asthma. On each study day, subjects underwent histamine challenges at 1 1 2 hours before, and 1 2 , 2, 4, 6, and 8 hours after inhaling one of the three test-drug treatments. Both drugs produced significant bronchodilatation at 30 minutes through 4 hours and significant effects on airway reactivity at 30 minutes through 2 hours ( p < 0.05). Bitolterol also produced small but significant bronchodilator effects at 6 hours and effects on airway reactivity at 4 hours ( p < 0.05). Effects of bitolterol on airway reactivity diminished significantly more slowly than effects of albuterol in subjects with baseline provocative concentration causing a 20% fall in FEV 1 ≥1.0 mg/ml of histamine (half-life of biologic effect 1.37 versus 0.92 hours; p < 0.05) but not in subjects with baseline provocative concentration causing a 20% fall in FEV 1 ≤1.0 mg/ml (half-life of biologic effect of 1.01 versus 1.00 hours; p > 0.05).