In the classic work on comparative neuroanatomy by Kappers, Huber and Crosby (1936) it is noted, possibly uniquely for a group of mammals, that the cetacean spinal dorsal horn does not have a region equivalent to the substantia gelatinosa (SG). In view of adaptations of these animals to an aquatic environment, their somatosensory system may also show unique specialisation. This preliminary anatomical survey was conducted to explore the types of primary afferent present in a typical small cetacean.A stranded harbour porpoise was humanely killed and a post-mortem carried out 48 hours later. Samples of peripheral nerves, dorsal root ganglia (DRG), dorsal roots and spinal cord were collected and fixed by immersion in 4% paraformaldehyde for 48 hours. Peripheral nerve and dorsal root samples were embedded in Araldite and semi-thin sections prepared and stained with toluidine blue. Ultrathin sections of the dorsal roots were prepared for electron microscopic analysis. Spinal cord and DRG sections, from wax embedded or frozen blocks, were stained histologically or immunocytochemically.The DRG contained both small and large neurones. Immunochemical staining demonstrated that the majority of the small neurones contained the neuropeptides substance P and calcitonin gene related peptide (CGRP). The dorsal roots contained unmyelinated axons, although at a relatively low density. As described in earlier studies, the spinal cord at the thoracic and cervical levels had a relatively small dorsal horn and no obvious layer corresponding to the SG. However, Nissl and silver staining do reveal a region of smaller neurones in an area with a low density of myelinated fibres that could correspond to LII-LIII. In contrast to the pattern seen in the rodent, CGRP stained central terminals formed a single band, as though LI/LIIo and LIIIV were not separated by a CGRP free LIIi. A band of distinct larger neurones on the edge of the dorsal horn corresponds to LI.These observations demonstrate that cetaceans do have C-fibre primary afferents containing CGRP that, in other species, have been implicated in nociception. However, other populations of unmyelinated afferents may be reduced or absent.