The so-called cystitis due to cyclophosphamide (Cytoxan) is caused by direct contact of the mucosa with alkylating metabolites in acid urine. These alkylating metabolites can be inactivated by instillation of cysteine into the urinary bladder. The cytostatically active metabolites of ifosfamide (Holoxan), a derivative of oxazaphosphorine, are eliminated by the kidneys as well. Their special toxicity is much higher than the toxicity of Cytoxan. The alkylating metabolites of ifosfamide cause urological complications essentially in supravesical areas (tubulopyelo-ureteritis). Some clinical trials demonstrate that increase of diuresis and alkalinization of urine by orally administered Uralyt-U are able to decrease concentration and aggressiveness of those metabolites.