The present study investigated the effects of Sinitang (Japanese name: Shigyaku-to--a traditional Chinese medicine), on microcirculatory disturbances induced by endotoxin in rat mesentery. The changes of arteriolar diameter, the velocity of red blood cells in arterioles and venular microcirculation after endotoxin injection (6 mg x kg(-1), i.v.) were observed by videomicroscopy. Mean arterial pressure and heart rate were monitored continuously during the experiments. Sinitang significantly prevented the decrease of mean arterial pressure, controlled the reduced velocity and also, apparently inhibited the leukocyte extravasation across venules. However, there were no significant changes in the arteriolar diameter and the heart rate in all groups treated with or without Sinitang. The results indicate that Sinitang has protective effects to improve the microcirculatory disturbances induced by endotoxin in rat mesentery.