Using immunocytochemistry with an antibody raised to a specific rat bradykinin B1 receptor sequence, we showed that the B1 receptor was expressed in the naive rat sensory nervous system. B1 immunoreactivity was seen in laminae 1 and 2 of the dorsal horn of the spinal cord, where primary afferents terminate, and on peripheral nerve terminals in the bladder. B1 receptor was co-expressed preferentially with IB4 positive, but not calcitonin gene-related peptide (CGRP) containing C-cell bodies in the dorsal root ganglion. B1 activation has an important role in the hyperalgesia associated with inflammation, but the site of action of B1 antagonists has generally been believed to be on peripheral, non-neuronal cells. The striking distribution of B1 receptors on sensory neurones suggests that a direct action of B1 activators on the nervous system may also contribute to hyperalgesia.