BACKGROUND: The pain-inhibitory effects of spinal cord stimulation (SCS) may be exerted at two alternative or complementary levels, segmentally or supraspinally. However the actual pathways, site of action, and synaptic relays are poorly understood. No data is available which concerns the changes in cord dorsum potential (CDP) associated with a single neuronal level, after SCS. METHODS: SCS was performed in normal and spinalized cats. At the lumbosacral enlargement, CDP and extracellular single cell activity in response to electrical stimulation of Asigma- or C-fiber of the dorsal root or sciatic nerve were recorded. RESULTS: The resulting CDP consisted of characteristic waves of Asigma- and C-fiber with a different time latency. CDP sno significant differences in the amplitude of Asigma- and C-fiber wave between the normal and spinalized cats. In both groups, CDP showed decrease in the amplitude of C-fiber wave. Single cell responses were either increased or decreased after SCS. The C- response changed more marKedly than the A-response in both the normal and spinalized cats. In the bicuculline administered cats, single cell responses increased after SCS, but no change was found in the amplitude of CDP. CONCLUSIONS: The above results might indicate that SCS suppresses C-fiber transmission of nociceptive electrical stimuli via a segmental inhibitory mechanism, and that SCS is more effective in blocKing the transmission of nociceptive electrical stimuli via the C-fiber than Asigma-fiber.