Identification of mechanisms for the increased susceptibility of infants to toxigenic E. coli diarrhea. His study of the endogenous intestinal peptides guanylin and uroguanylin has resulted in an understanding of their secretory, diuretic, and anti-nociceptive functions. His studies provided, in part, the basis for the development of pharmacologic agonists of the guanylin/uroguanylin receptor, e.g., linaclotide, now used to treat severe constipation and irritable bowel syndrome. His clinical research relates to vaccines for diarrheal diseases including E. coli and cholera diarrhea.