A model of burn shock was reproduced in rat. The effects of crystal No 4 of Polygonum cuspidatum (p. c.) on microcirculation of spinotrapezius muscle in rat with burn shock were observed with a special Hitachi TV set with magnification of 4000x. The changes in water content in tissues of lung and burned skin were measured. The survival time of burned animals was recorded. The aggregation of WBC and the degree of tissue damage in lung were examined in pathologic slides. The results showed that during burn shock the number of adhesive WBC in venules was about 8 times more than normal, the amount of open capillaries was reduced by 3/5 of normal. There were apparent aggregation of WBC and tissue damage in the lung. The number of adhesive WBC was decreased by 80%, the amount of open capillary returned to near normal, and the aggregation of WBC and the degree of tissue damage in the lung were alleviated by administration of crystal No 4 of Polygonum cuspidatum. The survival time in p. c.-treated group was prolonged 1.9-fold of that in n.s.-treated group. The results indicated that the decrease of WBC adherence was caused by, on the one hand, the increase of driving force and wall stress after treatment of p.c., and on the other hand, p. c. might affect some humoral factors which promoted WBC adherence.