It is a fundamental principle of vertebrate neuronal organization that sensory fibers are restricted to dorsal roots and motor fibers to ventral roots. Recent evidence, however, indicates that there are many sensory fibers in ventral roots. The present report shows that stimulation of these fibers activates neurons in the dorsal horn. This provides evidence at the single-cell level for the importance of ventral root afferents and provides an explanation for the clinical phenomenon of recurrent sensibility.