A novel (S,S)-R(2)eddip ester, O,O'-diisopentyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate dihydrochloride (1) was synthesized and characterized by IR, H-1- and C-13-NMR spectroscopy, mass spectroscopy and elemental analysis. In vitro antitumor action of 1, and two more R(2)eddip esters, dialkyl (S,S)-ethylenediamine-N,N'-di-2-propanoate dihydrochlorides, obtained before (alkyl = n-Bu or n-Pe, 2 and 3, respectively), was determined against cervix adenocarcinoma (HeLa), human melanoma (Fem-x), human chronic myelogenous leukemia (K562) cells, and a non-cancerous cell line human embryonic lung fibroblast (MRC-5), using the microculture tetrazolium test MTT assay. Esters 1-3 showed higher cytotoxicity and better selectivity in comparison to cisplatin, used as reference compound. The highest activity was expressed by 1, with IC50(Fem-x) value of 1.51 +/- 0.09 mu M.