Increased numbers of mast cells and their products have been linked to symptom onset and severity in patients with chronic diarrhea and abdominal pain. Although mast-cell inhibition ameliorates clinical manifestations and reduces mucosal inflammation, underlying molecular mechanisms remain unknown. Experiment Overall Design: Diarrhea-irritable bowel syndrome (d-IBS) patients were studied at baseline, or 6 months after natural evolution (control) or oral cromoglycate treatment. Jejunal biopsies were subjected to chip analysis (Affymetrix Human Genome U133 Plus 2.0 GeneChips).