Abstract: Pharmacogenetics was used to evaluate the effect of polymorphisms in select candidate genes on the response of patients with chronic constipation to tegaserod (Zelmac®/Zelnorm®). The analysis identified twelve single nucleotide polymorphisms (SNPs) in six genes (HTR4, HTR3B, MLN, AQP3, SLC12A2, SCNN1A) that were associated with at least a 60% response rate to tegaserod and an odds ratios of 5 or greater (compared to placebo) after 4 weeks of treatment. The identified genes display a wide range of different functions, including serotonin signaling, secretion and motility, all of which are important in maintaining the normal function of the gastrointestinal tract. Thus, these data imply that chronic constipation may result from a variety of pathophysiological mechanisms related to variants in the above identified genes, all of which respond well to treatment with tegaserod.