Inflammatory bladder disorders such as interstitial cystitis (IC) deserve attention since a major problem of the disease is diagnosis. IC affects millions of women and isClinical and animal models of acute and chronic urinary bladder inflammation have provided several lines of evidence suggesting a central role of mast cells, sensory nerves, and neurokinin (NK)-1 receptors. Fundamental work regarding the participation of sensory nerves and mast cells in cystitis provides indirect evidence, such as increased numbers of mast cells in the detrusor and submucosa, and morphological evidence of mast cell activation and degranulation. [1][2][3][4] In addition, the extensive tissue remodeling seen in some clinical forms of bladder inflammation such as interstitial cystitis, 4 along with increased urinary levels of histamine and tryptase 5 suggest a role for mast cells. Because both mast cells 6 -8 and NK-1 receptors are increased in bladder biopsies of interstitial cystitis (IC) patients, 9,10 it is tempting to propose a role for sensory peptides-mast cell communication in the pathogenesis of this disorder.Experimentally, we have used classical morphometric analysis and microarray technology to determine the role of mast cells, NK-1 receptors, and bacterial toxins in animal models of cystitis. Time-course experiments indicated early and late genes involved in bladder inflammatory responses. 11 The availability of mice genetically deficient in neurokinin-1 receptor (NK-1R ÏȘ/ÏȘ ) allowed us to propose a mandatory role of SP receptors in cystitis. 12 We also determined genes that depend on the presence of tissue mast cells for their expression by comparing inflammatory responses in mast cell-deficient (Kit W /