Six new mixed ammine/ethylamine platinum(II) complexes with carboxylates [Pt(II)(NH(3))(C(2)H(5)NH(2))X(2)] (a-f) (X=CH(3)COO(-), CH(2)ClCOO(-), C(6)H(5)-COO(-), p-CH(3)-C(6)H(4)-COO(-), p-CH(3)O-C(6)H(4)-COO(-), p-NO(2)-C(6)H(4)-COO(-)) (a-f) have been synthesized and characterized by elemental analysis, conductivity, spectra techniques (IR, UV and (1)H NMR). The cytotoxicity of the complexes was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The relative reactivity of leaving groups of complex (c) with G-actin was determined spectrophotometrically at 412 nm. The results show that the complexes (a-f) confer substantially greater cytotoxicity against EJ and HL-60 than the other carcinoma cell lines, moreover, the cytotoxicity of complexes (c-e) is equal to that of cisplatin against HL-60, and the cytotoxicity of complex (c) is also equal to that of cisplatin against EJ. However the complexes (a-f) are significantly less potent than cisplatin against BGC-823, HCT-8 and MCF-7. The reactivity of leaving groups decreases in the sequence: cisplatin > c > carboplatin. The results suggest that ammine/ethylamine platinum(II) complexes with carboxylate anion as leaving group have selectivity against carcinoma cell lines. When leaving group is aromatic carboxylate ion, the complexes have better cytotoxicity, moreover, the substitution radical in benzene ring also influences cytotoxicity. (C) 2008 Elsevier Masson SAS. All rights reserved.