The present study was carried out to determine the effects of intracisternal administration of three doses of bombesin (0.001, 0.01 and 0.1 μg) on afferent somatosensory transmission in single neurons of the spinal trigeminal nucleus of anesthetized rats. Lower doses (0.001 μg) of bombegin did not change the afferent sensory transmission. Medium doses (0.01 μg) of bombesin significantly (p p<0.01) facilitated afferent sensory transmission in the 6 to 30 min post-drug period, but higher doses (0.1 μg) inhibited responsiveness of spinal trigeminal neurons in the 16 to 35 min post-drug period. The results indicate that endogenous bombesin-like peptide present in the spinal trigeminal nucleus may participate in the processing of the somatosensory information arising from the face.