The tools of electrophysiology and molecular biology have opened new insights in the nature and function of colonic K⁺ channels. In this review we have tried to give an overview on the present knowledge about K⁺ channels, their physiological role, their regulation and their molecular identity on the background of colonic function. The enormous number of excellent work in the colon field makes the citation list inevitably incomplete. We apologise for this. The rapid progress in K⁺ channel research promises to reduce the gaps in present knowledge soon. It might also result in new perspectives on presently controversially discussed aspects. Fields of special interest are the K⁺ channels in human colon and the luminal membrane in general. Only the precise knowledge of single channel properties in the intact tissue allows the interpretation of channel attributes in the expression systems. Several recent findings speak in favour of the existence of modular channels consisting of several different subunits and regulatory proteins. The concerted application of molecular biology and epithelial physiology might help to discover the co-operating proteins.