The molecular biology of brush membrane transport proteins continues to be defined. This review summarizes recent advances in our knowledge of electrolyte transport in this respect. An increasing understanding of brush border transport is now being used to identify ways of modifying carriers pharmacologically; the activity of the chloride channel in cystic fibrosis and in secretory diarrheal states has recently received attention. Modulation of transport by peptides (atrial natriuretic peptide and epidermal growth factor), mast cells, and dietary factors is reviewed. Refinements to the clinical management of acute diarrhea by modification of oral rehydration solutions remains a priority and continues to receive attention.