Hospital and communal waste water differ with respect to their content of specific chemical substances like disinfectants or medicaments. Some medicaments are metabolized poorly by patients after administration. Antineoplastic substances are supposed to be cancerogen, mutagen and fetotoxic and embryotoxic substances. At the present there is no information available about their behaviour in the environment. Therefore the biodegradation of ifosfamide and cyclophosphamide was investigated by using the Closed Bottle Test (OECD 301 D). Both the structural isomeric antineoplastics were not biodegraded at a concentration of 5 mg/l in the Closed Bottle Test within 28 days (''not readily biodegradable''). A prolongation of the test up to 57 days did not alter the result. Abiotic elimination was neglectible. Cyclophosphamide and ifosfamide were not found toxic against waste water microorganisms. Further investigations about the elimination of ifosfamide and cyclophosphamide in the process of waste water treatment are necessary to get more knowledge about the possible risk connected with these substances