The present study was designed to test the effect of a substance P (SP) antagonist, [D-Arg1, D-Trp7,9, Leu11]substance P (Spantide), on spontaneous efferent activity of adrenal sympathetic nerve and the two A- and C-sympathetic reflex components evoked in adrenal sympathetic nerve by stimulation of myelinated A- and unmyelinated C-afferent nerve fibers of a hindlimb nerve, respectively, in anesthetized rats. The spontaneous adrenal nerve activity and both of the A- and C-sympathetic reflex components were proportionally reduced by intrathecal application of the SP antagonist (0.038-0.76 nmol), although the same doses did not affect A- and C-somatic reflex components. These data suggest that the SP antagonist has a greater effect on SP-containing neurons related to the generation of spontaneous activity of sympathetic neurons and somato-sympathetic reflex pathways than on SP-containing primary somatic afferent nerves and somato-somatic reflex pathways.