The paper presents the study of the excretion of sulfated glycosaminoglycans (GAG) in the urine of rats in experimental hemorrhagic cystitis induced by cyclophosphamide and treated with glycosaminoglycan replacement therapy. Rats were given intraperitoneal injections of cyclophosphamide at a dose of 100 mg per 1 kg body weight and subsequently treated with intragastric administration of the combined preparation of glycosaminoglycans containing glucosamine hydrochloride and chondroitin sulfate at a dose of 10 and 100 mg per 1 kg of body weight. Within 24 or 72 hours after cystitis induction there was a statistically significant increase in urinary GAG excretion. The study also found a decrease (from 1.34 to 1.22 mg/dL) in urinary GAG within 0 to 72 hours following induction of acute cystitis without glycosaminoglycan therapy. In the subchronic model of inflammation in the bladder, upon repeated administration of low doses of cyclophosphamide (50 mg/kg), decrease in urinary GAG within 0 to 72 hours (1,32±0,13 mg/dL) as well as increased excretion after 96 hours at a concentration of 2,29±0,13 mg/L after initiation cystitis were found.