Of the developments which have occurred in this field in the last few years, several stand out. The importance of a 'shunt' pathway for ion transport, which passes between rather than through, the epithelial cells, and its role in determining the differing transport characteristics of jejunum, ileum and colon has been recognized. The links between sodium transport and the transport of several other solutes and ion-exchange processes have been examined in some detail. The role of intestinal secretion in the pathogenesis of many types of diarrhoea has been elucidated and the exciting advances in our knowledge of the biochemical basis for intestinal secretion are providing leads for the potential pharmacological control of secretory diarrhoea. This review will focus on these particular topics.