Airway responsiveness to inhaled histamine was examined in two groups of carefully selected patients with nonasthmatic chronic obstructive airways disease (COAD). Twelve patients with chronic bronchitis and airflow obstruction but little emphysema and 13 with predominantly emphysema and airflow obstruction but little bronchitis were selected based on history, chest roentgenogram, and diffusing capacity for carbon monoxide (Dsb). Emphysema patients had less cough, less sputum, less chronic bronchitis, lower Dsb, and more radiographic evidence of vascular deficiency. There was no difference in anthropometric features, smoking history, atopic skin sensitivity, hemoglobin, blood eosinophilia, PaO2, PaCO2, ECG, lung volumes, or expiratory flow rates. The two groups had similar airway responsiveness to inhaled histamine; the geometric mean provocation concentrations producing a 20 percent FEV1 fall (PC20) was 0.56 mg/ml for the bronchitis patients and 0.28 mg/ml for the emphysema patients (p greater than 0.20). Regression of log histamine PC20 vs percent predicted FEV1 showed a high correlation in both groups (r = 0.73, p less than 0.01 in bronchitis and r = 0.79, p less than 0.001 in emphysema). The regression lines were almost identical. These data suggest that in COAD bronchial responsiveness to inhaled histamine is mainly due to the altered airway geometry, and that there is no difference in histamine responsiveness between patients with emphysematous COAD and nonemphysematous COAD with chronic bronchitis.