Dysregulation of gallbladder ion and water absorption and/or secretion has been linked to cholesterol crystal and gallstone formation. We have recently demonstrated that obese, leptin-deficient (Lep ^ob) mice have enlarged gallbladder volumes and decreased gallbladder contractility and that leptin administration to these mice normalizes gallbladder function. However, the effect of leptin on gallbladder absorption/secretion is not known. Therefore, we sought to determine whether leptin would alter the expression of genes involved in water and ion transport across the gallbladder epithelium. Affymetrix oligonucleotide microarrays representing 39,000 transcripts were used to compare gallbladder gene expression profiles from 12 week old control saline-treated Lep ^ob and from leptin-treated Lep ^ob female mice. Leptin administration to Lep ^ob mice decreased gallbladder volume, bile sodium concentration and pH. Leptin repletion upregulated the expression of aquaporin (AQP) water channel 1 by 1.3 fold and downregulated AQP4 by 2.3 fold. A number of genes involved in sodium transport were also influenced by leptin replacement. Epithelial sodium channel and sodium hydrogen exchangers 1 and 3 were moderately downregulated by 2.0, 1.6 and 1.3 fold, respectively. Carbonic anhydrase IV which plays a role in the acidification of bile was upregulated 3.7 fold. In addition, a number of inflammatory cytokines which are known to influence gallbladder epithelial cell absorption and secretion were upregulated. Thus, leptin, an adipocyte derived cytokine involved with satiety and energy balance, influences gallbladder bile volume, sodium, and pH as well as multiple inflammatory cytokine genes and genes related to water, sodium, chloride and bicarbonate transport.