Potassium channels that are inhibited by intracellular ATP (ATPi) were first identified in ventricular myocytes, and are referred to as ATP-sensitive K+ channels (i.e. KATP channels). Subsequently, K+ channels with similar characteristics have been demonstrated in many other tissues (pancreatic β-cells, skeletal muscle, central neurones, smooth muscle). Approximately one decade ago, KATP channels were cloned and were found to be composed of at least two subunits: an inwardly rectifying K+ channel six family (Kir6.x) that forms the ion conducting pore and a modulatory sulphonylurea receptor (SUR) that accounts for several pharmacological properties. Various types of native KATP channels have been identified in a number of visceral and vascular smooth muscles in single-channel recordings. However, little attention has been paid to the molecular properties of the subunits in KATP channels and it is important to determine the relative expression of KATP channel components which give rise to native KATP channels in smooth muscle. The aim of this review is to briefly discuss the current knowledge available for KATP channels with the main interest in the molecular basis of native KATP channels, and to discuss their possible linkage with physiological functions in smooth muscle.