The contractile action of barium (Ba²⁺) was investigated in the arterial strip of rabbit renal artery. The helical strip of isolated renal artery was immersed in the Tris-buffered Tyrode s solution equilibrated with 100% O² at 37℃ and its isometric tension was measured. Ba²⁺-induced contraction of arterial strip was dose-dependent and its maximal tension corresponded to 92.1±4.5% of tension by K⁺(100 mM). Ba²⁺-induced contraction did not show the tachyphylactic phenomenon in the normal Tyrode s solution. Ba⁺² induced the tonic contraction in the Ca²⁺-free tyrode s solution and that was increased by the extracellula addition of Ca²⁺. During the repeated exposure of the same dose of Ba²⁺ (10 mM) in the Ca²⁺-free Tyrode s solution, Ba²⁺-induced contraction was progressively decreased. Even though the intracellular NE-and caffeine-sensitive Ca²⁺ was depleted, Ba⁺² induced the tonic contraction. After the pretreatment of lanthnum or verapamil, Ba⁺² did not induce contraction. Ba²⁺-inducedcontraction was suppressed by extracellular K⁺ in the normal Tyrode s solution and that was dependent on K⁺ concentration. Suppressive effect of K⁺ (14 mM) on the Ba²⁺-induced contraction was also dependent on the intracellular Ca²⁺ concentration. From the above resuts, it is suggested that Ba⁺² activate indirectly the contractile process by promoting the mobilization of intracellular Ca²⁺ and the influx of extracellular Ca²⁺. It is also suggested that action of Ba⁺² on the Ca²⁺-activated K⁺ channel can result in the depolarization of cell membrane in the rabbit renal artery.