Chengqi mixture (CM) is a Chinese herbal mixture valuable in treating acute peritonitis. The anti-inflammatory action of Chengqi mixture was investigated on the synthesis of leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) of peritoneal macrophages in rats. These mediators were determined by Reverse Phase-High Performance Liquid Chromatography. The ultraviolet absorbance of LTB4 was 280 nm

and of 5-HETE was 235 nm. The results indicated different concentrations of CM significantly inhibited the synthesis of LTB4 compared with the control (P<0.01

n=16) and were dose dependent from 0.15 to 10 g/L. The inhibitory rate of CM for the LTB4 exceeded 95% and for 5-HETE was about 70% at the dose of 5 g/L. The inhibitory rate of CM was equal to that of the flufenamic acid group in which the final concentration was at 10−4M. The half inhibitory rates (IC50) of CM for LTB4 and that for 5-HETE were 0.8 g/L and 1.1 g/L respectively. It is suggested that the anti-inflammatory actions of CM was related to the inhibition of synthesis of LTB4 and 5-HETE from arachidonic acid via 5-lipoxygenase in macrophages.