The alkylating agents bendamustine and melphalan are currently used in the treatment of various tumoral diseases. In order to increase their antitumor potency and tumor selectivity both compounds were integrated in structure-activity relationship studies including new drug carrier systems. Here we describe the synthesis and the cytotoxicity of new bivalent bendamustine and melphalan derivatives. Two molecules each esterified with N-(2-hydroxyethyl)maleimide were connected by diamines with various chain lengths (n=6, 7, 8, 12). It was supposed that these conjugates (5a-d, 10a-d, 11a-d) cause cytotoxic effects preferred as bivalent drug. Indeed the cytotoxicity of the new compounds increased compared to bendamustine and melphalan as determined in concentration-dependent in vitro assays using the human MCF-7 and MDA-MB-231 breast cancer cell lines.