The capsaicin (3 microM)-evoked release of the immunoreactive calcitonin gene-related peptide (iCGRP) from dorsal-half slices of the rat lumbar spinal cord was substantially reduced in slices from rats which had undergone dorsal rhizotomy. This suggests that the release is elicited mainly from the nerve terminals of primary afferents. The release was significantly increased in slices from adjuvant arthritic rats compared with those from control rats. This suggests that the amount of iCGRP in a capsaicin-sensitive pool of the nerve terminals of primary afferents is elevated by adjuvant arthritis. Since adjuvant arthritis is known to cause an enhancement of biosynthesis and axonal flow of iCGRP in primary sensory neurons, the present results imply an increased release of iCGRP from the central terminals of the primary afferents in the adjuvant arthritic rat.