In situ hybridization was used to study the expression and localization of tumor necrosis factor (TNF) mRNA in liver of rats after burn. The results showed that the Kupffer cells expressed TNF mRNA in normal rats. After burn, the number of positive expression cells increased quickly, the expression reached max-mum at 6h postburn, and there were no significantly different with normal at 24h postburn. The dynamic changes of number of TNF mRNA producing cells was similar to that of the portal plasma endotoxin level. Kupffer cells located in sinusoid surrounding portal vein expressed TNF mRNA especially at 6h-12h postburn. Also the sinusoid endothlial cells and infiltrative inflammation cells surrounding portal vein were the TNF mRNA-producing cells, this changes appeared significantly at 12-24h postburn. The results suggested that the endotoxin originated from gut may be the principal stimulator for expression of TNF mRNA. The expression of endothlial cells and neutrophils suggested that these cells had been activated. So the endothlium, neutrophils and Kupffer cell play an important role in the pathogenesis of the endotoxin-induced live injury.