Objective To study the effect of FK506 pretreatment on endotoxin shock induced by LPS. Methods 155 mice of the Kunming strain were randomly divided into LPS group (n=80) and LPS|FK group (n=75). An endotoxin shock model of mice was reproduced by an intraperitoneal injection of LPS (25ml/kg for each mouse). Beginning from 2 days before the reproduction of the model, each mouse of the LPS+FK group were given 20ml/kg of FK506 q 12 h, by gastric gavage while animals of the LPS group were given an equal amount of 0.9% sodium chloride solution in the same way. The survival time of 20 mice of the LPS group and 15 mice of LPS+FK group was observed. 10 mice of each group were sacrificed at 0,0.5,2,4,6 and 8 hours after the injection of LPS, respectively. Blood samples were collected and serum TNF-? and IL-1?, contents, and activiry of ALT and AST were determined. The ratio of the wet weight and dry weight (W/D) of the lung was calculated, and the histopathology of the lung and the liver was studied. Results The mean survival time was longer and the 72h survival rate in mice of LPS+FK group was higher, but the serum ALT and AST activity and serum TNF-? and IL-1? contents were lower than those of LPS group at each time point. The W/D ratio of the lung in animals of both groups at 4,6 and 8 hours after the injection of LPS was greater than that at 0 hour (P