Intracellular free Ca²⁺ contributes to regulation of various events occurring in vascular smooth muscle cells. One of these events is modulating the membrane iou currents. Single smooth muscle cells were isolated from rabbit mesenteric artery. Three kinds of Ca²⁺-activated current were studied with the patch clamp method. Ca²⁺-activated K⁺ current with a large oscillation was recorded in the depolarized potential range. The single channel conductance of this current was about 250 pS. It was abolished by replacing intracellular K⁺ with Cs⁺. A Ca²⁺-activated nonselective cation current was observed in both the depolarized and hyperpolarized potential ranges. And it was blocked by replacement of extracellular Na⁺ with N-methylglucamine (NMG) or extracellular application of Cd²⁺. Ca²⁺-activated Cl^- current was revealed in the whole voltage range and was blocked by niflumic acid. These results indicate that at least three kinds of Ca²⁺-activated ionic currents exist in smooth muscle cells from rabbit superior mesenteric artery.