Substance P, a physiologically potent neuropeptide is known to participate in the sensory, and especially nociceptive, transmission of neural impulses. On histologic grounds, the nerve terminals of the sinuvertebral nerve formerly have been suggested to be sensory in character and to mediate the low-back pain syndrome. Samples of paramedullary ligamentous structures were collected on disc operations. A positive immunoreaction as an indicator of substance P was confirmed in some nerve terminals of the posterior longitudinal ligament. Neither the yellow ligament nor the intervertebral disc showed such nociceptive-type nerves.