Hospital and communal waste water differ with respect to their content of specific chemical substances like disinfectants or medicinal drugs (Gartiser et al. 1996). Because the active substances of certain drugs are often metabolized poorly by patients after administration, they are excreted into waste water. Antineoplastic substances are supposed to be very stable (Allwood and Wright 1993; Lunn et al. 1989). Moreover, antineoplastics are known to be often carcinogenic, mutagenic, fetotoxic and embryotoxic (Allwood and Wright 1993). Till now, in the European Union (EU) medicaments need not be examined for their environmental properties: only a draft of a guideline exists, according which the examination of biodegradability is one of the important steps for evaluating the environmental impact of pharmaceuticals. Consequently, there are little information regarding their biodegradation in the aquatic environment. Traces of the antineoplastics ifosfamide and cyclophosphamide as well as other pharmaceuticals were detected in the sewage water of hospitals (Steger-Hartmann et al. 1996, Stan et al. 1994). Examination of their biodegradability with the Closed Bottle Test conducted previously showed that these antineoplastics are “not readily biodegradable” (Kümmerer et al. 1996). We examined the biodegradability of other antineoplastics with different chemical structures and mechanisms of action than ifosfamide and cyclophosphamide, which alkylate after activation by eukaryotic cells: we studied the biodegradation of the intercalating anti-tumour agent mitoxantron hydrochloride and treosulfane, which alkylates without activation by eukaryotic cells using the Closed Bottle Test (OECD 301 D 1992). The testing of the biodegradation of these two antineoplastics is necessary to obtain knowledge about the possible risk for man and environment associated with these substances.