Somatostatin is measured in the rat spinal cord by radioimmunoassay. Levels are higher in more caudal spinal segments, much higher in gray than in white matter, and highest in the dorsal horn. Dorsal root ganglionectomy decreases somatostatin levels in the dorsal cord, supporting the proposed role for this peptide as a primary sensory neurotransmitter of modulator. However, somatostatin levels also decrease both rostral and caudal to spinal transection, indicating the probability of ascending and descending somatostatin pathways with the spinal cord. Met-enkephalin levels were not altered by these surgical procedures and Substance P levels were modified significantly only after dorsal root ganglionectomy.