Cook is a leading international figure in research on exocrine epithelia. He has made many important contributions to the understanding of the role of ion channels in exocrine gland function, but is particularly known for his more general discovery that epithelial Na+ channels and other transporters are regulated by the intracellular concentrations of Na+ and CI-. Prior to Cook's work, epithelial Na+ channels had been thought to be regulated by the extracellular concentration of Na+. In an elegant and technically impressive series of studies, he showed that these channels were in fact regulated by intracellular Na+ and CI- and elucidated the molecular mechanisms underlying these regulatory systems. His work has led to an important new model for the understanding of how the concentrations of ions such as Na+ and CI- are maintained stable within the cytosol, a model with important implications for the understanding of epithelial function both in health and in disease states such as hypertension and cystic fibrosis. His other major contributions include the demonstration that respiratory pathogens such as influenza virus inhibit the Na+ channels in lung epithelia and the discovery of a novel cytocortical clock that regulates the activity of K+ and CA2+ channels during the cell cycle.