To study the effective site of bronchodilators in patients with chronic obstructive pulmonary disease (COPD), a catheter tip micromanometer sensing lateral pressure of the airway was wedged into the right lower lobe of a bronchus, 3 mm inner diameter, in 14 patients with COPD. We simultaneously measured mouth flow, transpulmonary pressure (PL) and intra-airway lateral pressure during quiet tidal breathing. Total pulmonary resistance (RL) was calculated from PL and mouth flow, and central airway resistance (RC) was calculated from intra-airway lateral pressure and mouth flow. Peripheral airway resistance (RP) was obtained by the subtraction of RC from RL. This technique permitted identification of the site of changes in airway resistance. Atropine sulfate (5 mg/ml) was continuously inhaled during tidal breathing for 1 min by seven patients (Group A), and the other seven patients (Group B) inhaled fenoterol (1 mg/ml) for 1 min. The doses that were actually delivered were 0.75 mg for atropine sulfate and 0.15 mg for fenoterol. The baseline resistances of RC and RP were 3.9 +/- 0.8 and 3.7 +/- 0.6 cm H2O/L/s in Group A, and 4.3 +/- 0.5 and 3.5 +/- 0.4 cm H2O/L/s in Group B, respectively. Both atropine sulfate and fenoterol significantly decreased RL by an average of 2.4 and 2.6 cm H2O/L/s, and there was no significant difference between them (p greater than 0.20). The percentage decrease in resistance from the baseline values by fenoterol did not differ significantly between RC and RP (p greater than 0.20). However, atropine sulfate significantly decreased RC more than RP.(ABSTRACT TRUNCATED AT 250 WORDS)