Chemotherapy is a tool for killing fast proliferating cells, like most tumor cell lines, by means of therapeutic agents. Since the cell membrane is an efficient barrier for most chemical substances, many anti-cancer agents need to be applied in a high dose in order to reach a lethal level inside the cell. This in turn has implications for non-tumor cells yielding most of the known side effect of chemotherapy. There are perspectives for targeting drugs to the tumor in order to enhance the selectivity of the treatment, i.e. by means of magnetic field, liposomes or a tamers with high binding affinity to special cell lines.