1. Measurements of airways resistance and lung volume were made in sixteen patients with chronic bronchitis and ten patients without chest disease before and after intravenous propranolol administration.
2. The airways resistance of the patients with chronic bronchitis increased significantly after propranolol administration but in the control subjects there was no significant increase.
3. In the patients with chronic bronchitis the increases in airways resistance were greater when the initial values were high.
4. In seven of the patients with chronic bronchitis and seven further control subjects airways resistance was measured before and after intravenous thymoxamine administration.
5. The airways resistance of the normal subjects was unchanged by thymoxamine administration, but that of the patients with chronic bronchitis decreased significantly.
6. The results are consistent with the existence of bronchial alpha receptors in man. In patients with chronic bronchitis there are greater degrees of both alpha and beta bronchial sympathetic activity than in normal subjects. The greater the severity of the condition the greater is the degree of beta sympathetic activity. In considering the factors causing airways obstruction in chronic bronchitis sympathetic activity should be taken into account.