Abstract: The present invention relates to the use of selenium and/or a derivative thereof in combination with one or more cytostatics. It is the object of the present invention to provide a possibility of enhancing the effect of antitumor drugs, and to provide said drugs in a suitable form of administration. Said object is achieved by using selenium and/or at least one selenium compound for enhancing the effect of one or more cytostatics. This combination results in a synergistic, i.e. superadditive, enhancement of the effect. Furthermore, the present invention provides a kit containing selenium and/or at least one selenium compound and one or more cytostatics as a combination preparation for cytostatic therapy. The present invention can be used efficiently against various types of tumor cells, but especially against large-cell and small-cell bronchial carcinomas, adenocarcinomas, pancreatic carcinomas, prostatic carcinomas and hypemephromas.