['We investigated the role of Tamm-Horsfall protein in interstitial cystitis.', 'Urinary Tamm-Horsfall protein excretion was analyzed in interstitial cystitis patients and controls, and bladder biopsy specimens were stained immunohistochemically for Tamm-Horsfall protein.', 'Urinary Tamm-Horsfall protein levels in 28 women with interstitial cystitis were statistically significantly greater than those in 25 female controls. No positive staining for Tamm-Horsfall protein was demonstrated in the bladder tissue from 10 interstitial cystitis cases.'] Do increased urinary levels of Tamm-Horsfall glycoprotein suggest a systemic etiology of interstitial cystitis?