Immunohistochemical methods were used to study the distribution of substance P in the brain of the small-spotted dogfish (Scyliorhinus canicula). Substance P-like immunoreactive (SP-IR) cell bodies and fibers were widely distributed. In the telencephalon, sparse populations of SP-IR neurons are present in the olfactory bulbs, pallium, and subpallium. In the subpallium numerous SP-IR boutons form unusual coats ("pericellular appositions") on SP-immunonegative neurons. In the diencephalon numerous SP-IR cerebrospinal fluid-contacting neurons are present in the preoptic recess organ and organon vasculosum hypothalami. Numerous SP-IR fibers also run in the hypothalamus, although no immunoreactivity was observed in the habenulo-interpeduncular system. A terminal field of SP-IR fibers is present in the median eminence. In the mesencephalic tegmentum, SP-IR neurons were observed in the Edinger-Westphal nucleus. SP-IR fibers are present at high density in the basal tegmentum, forming a conspicuous tract. In the hindbrain, numerous SP-IR fibers were observed in the isthmal region, the trigeminal descending root, the visceral sensory area and commissural nucleus, and the visceromotor column. SP-IR fibers occur at high density in the substantia gelatinosa of the rostral spinal cord.