Magnetic stimulation of nervous elements is a new neurophysiological technique. It easily succeeds in stimulating the brain motor cortex. We applied this technique to the trigeminal motor system, recording responses in masseter muscles. The magnetic stimulations at 4 cm laterally to the vertex on the biauricular line elicited responses in the contralateral masseter due to activation of motor cortex or adjacent elements along the cortico-nuclear pathway. The ipsilateral responses to the same stimuli and to more lateral ones presented shorter latencies and they were ascribed to direct stimulation of the trigeminal nerve, probably its intracisternal portion. The latency values were 6.9 +/- 0.71 ms and 3.6 +/- 0.3 ms respectively.