The nerves supplying the spinal dura mater were studied in four human foetuses (16-22 weeks) with the acetylcholinesterase in toto staining method. The ventral spinal dura contains a dense, longitudinally oriented, nerve plexus, which receives its contributions from: (I) the sinuvertebral nerves, (II) the nerve plexus of the posterior longitudinal ligament, (III) the nerve plexus of radicular branches of segmental arteries. Dorsal dural nerves are much smaller in number, do not form an evident plexus and do not reach the medial region of the dorsal dura. The dorsal nerves are derived from the ventral dural plexus at the level of the "intersleeval" parts of the dura mater. The ventral dural nerves may extend up to eight segments, with a great amount of overlap between adjacent nerves. This may provide an anatomical substrate for the understanding of extrasegmentally referred dural pain. The curled bundles of nerve fibres of pathways (I) and (II) provide an adequate adaptation to displacements of the spinal dura mater during flexion and extension. Pathway (III) has not been described before. The described nerve plexuses may be of importance in elucidating the mechanisms of epidural therapies in back pain and peripheral vascular disease.