Experiments were performed on 42 urethane-anesthetized rabbits of both sexes. The rabbits were either spontaneously breathing or gallamine paralyzed and artificially ventilated. Efferent phrenic nerve activity was recorded with bipolar silver electrodes. The experiment results were as follows: Unilateral mechanical lesion of focal block by microinjection of lidocaine (2%, 1 microliter) in the ventromedial region of nucleus facialis (VMNF) consistently caused apneustic-type breathing associated with no significant changes in the rate of rise of inspiratory activity. The expiratory time (Te) was only slightly affected or not changed at all. Some increase in Te was present only when a very strong apneustic effect was evoked. Respiratory effects of focal block by lidocaine in the region of VMNF were not accompanied by changes in blood pressure. No significant changes in respiratory rhythm were observed when lidocaine is microinjected in the nearby regions of VMNF. The results suggest that VMNF appears to be involved in an inspiratory off-switch mechanism.