In order to elucidate the relationship between several structures of CNS and the vestibulo-sympathetic response (VSR) in rat, the technique of spike triggering average (STA) was used. The spike of the neuron which responded to the pendular rotation (pendular positive unit, PPU) was used to trigger the onset of averaged activities of the splanchnic nerve (SN). Making use of the spike of PPU of nucleus vestibularis medialis (NVM) as an indicator, the SN-STA had a latency of 33.28 +/- 3.1 ms. SN-STA triggered by PPU of reticular formation (RF) of caudal brain stem, a positive response with a latency of 11.13 +/- 0.91 ms was observed. SN-STA triggered by PPU of vestibulocerebellum, a positive response with a latency of 21.86 +/- 1.73 ms was observed. Our results suggest that the nearest supraspinal relay may be the nuclei of medical RF in caudal brain stem and the descending flow of VSR was probably transmitted by the slow conducted fibers of reticulo-spinal tract. According to the latency of SN-STA by PPU of vestibulo-cerebellum, the vestibulcerebellum possibly executed a polysynaptic mission between the transmission of VSR outflow from NVM to RF nuclei of caudal brain stem.