The antihyperalgesia effect of BmK AS, a novel sodium channel-specific polypeptide modulator from Chinese scorpion venom in rats was investigated in this study. PWLs (paw withdrawal latency) were increased to 150+/-28, 203+/-34 and 250+/-17% of the control by administration of BmK AS (10 microl) at the concentration of 0.001, 0.01 and 0.1 mg/ml in carrageenan-induced inflamed rats, respectively. Meanwhile, PWLs were enhanced to about 126+/-4, 132+/-4 and 140+/-6% of the control at the same applied concentration of BmK AS in normal rats. The results suggest that BmK AS can induce peripheral antihyperalgesia and antinociception, which probably by modulating the sodium channel on nociceptive afferent pathway.