To investigate the inhibiting effects of ketamine on arterial plasma TNF-? concentration and lung injury in septic shock rat. Method: 40 Wister rats were divided into five groups. 15mg?kg~(-1) endotoxin (LPS) was intravenously injected alone (group Ⅰ)or ip ketamine 50,100 and 200mg?kg~(-1) before LPS, then ketamine was infused at 10mg?kg~(-1)?min~(-1) (Ⅱ, Ⅲ and Ⅳgroup). TNF-? was assessed with ELISA, and at the same time the arterial blood oxygen tension and lung water content were measured. Result: In contrast to normal control level, arterial plasma TNF-? levels and lung water content increased and arterial oxygen tension decreased after LPS in group Ⅰ, but in the rats of giving ketamine, plasma TNF-? level decreased more than that in the rats of giving LPS alone (group Ⅰ), change of arterial blood oxygen tension and lung water content in former groups were better than that of later, in dosage-dependent way. Conclusion: Ketamine can dose-relatedly decrease TNF-? concentration and lung injury degree induced by endotoxin.