1. The effect of breathing anaesthetic aerosols (lignocaine 20% and bupivacaine 5%) on respiratory reflexes was studied in rabbits.
2. The cough reflex was blocked in every experiment.
3. The inflation reflex was abolished in eleven out of twenty-six rabbits given lignocaine aerosol and in fourteen out of fifteen rabbits given bupivacaine aerosol.
4. The deflation reflex was blocked pari passu with the inflation reflex.
5. The ventilatory response to histamine was sometimes blocked; more commonly it was partially preserved.
6. The ventilatory response to phenyldiguanide was never impaired and often enhanced.
7. Bronchoconstriction produced by electrical stimulation of the peripheral cut ends of the cervical vagus nerves was unaffected.
8. Block of the above respiratory reflexes was associated with slower, deeper breathing.
9. Bupivacaine has produced more consistent and reliable results than lignocaine; the effects were reversible in both cases usually within 30 min.
10. Plasma concentrations of both anaesthetics were usually below the generally accepted toxic concentrations in man.
11. Control experiments using intravenous infusions of the anaesthetics proved that none of the effects could have been produced by systemic effects of the absorbed anaesthetic.
12. No pathological changes were found in the airways on both macroscopic and microscopic examination.
13. The experiments show that it is possible to block respiratory reflexes whose afferents arise from the airways, and to preserve a reflex arising at alveolar level.