Berberine could reverse the phenylephrine-induced contraction of aortic strips of rabbits, but not those induced by histamine, serotonin and high-K. It showed no effect on the resting tension of the strips.Prazosin l ?M completely abolished the phenylephrine-induced contraction of the strips, but berberine 100 ?M could block 94 ? 9%.The IC50 of berberine and prazosin for phenylephrine-induced c-ontraction is 30 ?M and 0.2 ?M. The results suggest that the action of berberine is not similar to sodium nitroprusside, but is similar to prazosin, a selective ?1 adrenoceptor blocker, although its potency is less than prazosin.