The effects of single oral doses of pirbuterol 10 mg plus hydroxyzine 10 mg, and of pirbuterol 10 mg plus placebo, were compared in a single-blind cross-over trial in 17 adult patients with reversible airway obstruction. The initial bronchodilator response after the two treatments was similar, but mean specific airway conductance at 3, 4, 6 and 8 h, and mean FEV₁ and FVC after 3 and 4 hours, were significantly higher after pirbuterol + hydroxyzine than after pirbuterol + placebo. The mean thoracic gas volume measured at 3 and 4 h was lower after pirbuterol + hydroxyzine. Heart rate, blood pressure and a continuous ECG record did not differ after the two treatments. The findings suggest that the combination of pirbuterol and hydroxyzine brings about more prolonged bronchodilatation in patients with reversible airway obstruction than does pirbuterol alone.