The proinflammatory and lipopolysaccharide (LPS)-inducible cytokine tumor necrosis factor alpha (TNF-alpha) has been shown to enhance primary sensory nociceptive signaling. However, the precise cellular sites of TNF-alpha synthesis is still a matter of controversy. Therefore, we focused our study on TNF-alpha protein synthesis and expression patterns in spinal cord of controls and rats under systemic challenge with LPS. The Enzyme-linked immunosorbent (ELISA) assay showed that the protein level of TNF-alpha reached peak at 6 h. Double immunofluorescence revealed that LPS-induced expression of TNF-alpha exclusively located in a subpopulation of neurons, microglia and macrophages. These observations have demonstrated the production of this proinflammatory cytokine by spinal neurons, but the inherent mechanisms remain unknown. Further studies are needed to confirm the pathogenic role of tumor necrosis factor in the early stage of inflammation.