Tooth pulp stimulation in the cat evokes a jaw-opening reflex that is usually bilateral. We defined the location of fibers crossing to activate the contralateral reflex by making midline sagittal transections at peripheral and central levels in 11 anesthesized cats. A local midsagittal transection of the brain stem 2-4 mm above the obex selectively eliminated the contralateral reflex response. Midline sagittal transections of the maxilla, mandible, cervical cord, or upper brain stem did not. © 1981.