Glycosaminoglycans (GAGs) have been identified histochemically and biochemically in urothelium. They have been suggested to have an anti- adherence effect at the bladder surface important in the urothelial defence against bacterial and carcinogenic insult. The aim of this study was to investigate urinary GAGs excretion in patients with interstitial cystitis. Urinary GAG excretion was determined in patients with interstitial cystitis (n:34; 16 males, 18 females) and healthy subjects (n:34; 16 males, 18 females). Urinary GAG determinations were made by the dimethymethylene blue method. Student's t-test was used for statistical analysis of the results. Urinary GAG excretion was found to be elevated significantly in patients with interstitial cystitis (14.45±2.02 mg/g Cr) as compared to healthy subjects (10.11±2.3 mg/g Cr) (p<0.01). There was no significant difference in urinary GAG excretion between males and females in either the healthy subjects or in the patients. Determination of urinary GAG excretion may be an important non- invasive test in the investigation of patients with interstitial cystitis.