New studies continue to define how colonic absorption and secretion are regulated by intracellular pH, peptides, inflammatory mediators, laxatives, and antidiarrheal agents. Additional work has addressed the influence of aldosterone on electrogenic sodium absorption and has shown the importance of nutritional status in the action of vitamin A on thyroid hormone modulation of aldosterone action. There is further evidence implicating platelet-activating factor as a mediator of intestinal secretion in inflammatory bowel disease and in the mechanism of action of anthraquinone laxatives. The activity of peptide YY, pituitary adenylate cyclase-activating polypeptide, endothelin 1, and guanylin suggest that these peptides may have physiologic or pathophysiologic effects on colonic transport. Studies on methods to enhance the absorption of peptides through the colonic mucosa indicate that it may be possible to improve systemic bioavailability of peptides via this route of administration.