Catechin is a well-known flavonoid found in many food plants and often utilized by naturopaths for the symptomatic treatment of several gastrointestinal, respiratory and vascular diseases. Our aim was to explore the biological basis for the medicinal use of this flavonoid by investigating whether catechin exhibits any pharmacological activity on smooth muscle preparations. We found that catechin dose-dependently relaxes both spontaneous and high $K^{+}$ (80 mM)-induced contraction in rabbit jejunum, showing specificity for the latter by causing a rightward shift in the $Ca^{2+}$ dose-response curve. Similar results were observed with verapamil, a standard $Ca^{2+}$ channel blocker (CCB). Catechin also inhibited high $K^{+}$-induced contraction in intact smooth muscle preparations from rat stomach fundus, guinea-pig ileum and guinea-pig trachea. In rat aorta, catechin inhibited phenylephrine (PE, 1 ${mu}M$) and $K^{+}$-induced contractions in a similar fashion. In PE-contracted, endothelium-intact aorta, this vasodilator effect was partially blocked by $N_{grave{u}}$-nitro-L-arginine methyl ester and atropine, indicating activity at cholinergic receptors and possibly a CCB effect at higher doses of catechin. In guinea-pig atria catechin was found inactive. These data suggest that catechin may possess $Ca^{2+}$ antagonist activity - in addition to an endothelium-dependent relaxant component in blood vessels - thus providing a pharmacological basis for the efficacy of catechin in hyperexcitability disorders of gastrointestinal, respiratory and vascular smooth muscle.