The aim of this study is to investigate the hypotensive and vasodilator effects of daidzein sulfates, a water-solubility derivative of daidzein. Tail cuff blood pressure of spontaneously hypertensive rat (SHR) was measured with non-invasive Electro-Sphygmomanometer. An isometric tension of rat mesenteric artery ring segments was recoded in vitro on a myograph. The results showed that daidzein sulfates (20 and 40 mg/kg) could decrease blood pressure of SHR in single dose and multi-doses. Daidzein sulfates (1-100 microM) inhibited the contraction of rat mesenteric arterial ring segments induced by norepinephrine (NA) and 5-hydroxytryptamine (5-HT). Daidzein sulfates (100-1000 microM) inhibited arterial segment's contraction induced by KCl and CaCl(2). The concentration- contractive curves were shifted toward right in a non-parallel manner with decreased E(max.) Daidzein sulfaltes inhibited the extracellular Ca(2+)-dependent contraction. Daidzein sulfates of 100 and 300 microM significantly inhibited the contraction induced by CaCl(2) in Ca(2+)-free solution, which is an extracellular Ca(2+)-dependent contraction; but daidzein sulfates did not inhibit the intracellular Ca(2+)-dependent NA-induced contraction, in Ca(2+)-free solution. The results suggest that daidzein sulfates possess significant hypotensive and vasodilator effects which mainly derive from artery smooth muscle cells by inhibiting the receptor-mediated Ca(2+)-influx.