A characteristic feature of intestinal epithelia is their ability to secrete chloride (Cl sup -), a process that occurs mainly in intestinal crypts and is the critical transport event in secretory diarrhoea. Increased potassium (K+) channel activity in the basolateral membrane has an important role in the Cl- secretory process by hyperpolarising the cell and maintaining a favourable electrochemical driving force for Cl- exit at the apical membrane. We have shown, using patch-clamp techniques, that the basolateral membrane of human colonic crypt cells contains low conductance K+ channels that are voltage and calcium (Ca2+) sensitive and blocked by barium (Ba2+). These K+ channels are regulated by cytosolic cyclic adenosine monophosphate (cAMP) and Ca2+, intracellular second messengers that also stimulate Cl- secretion. This population of human intestinal K+ channels may be a target for the pharmacological control of Cl- secretory diarrhoea.