The preparation and characterization of the new 3,5-diacetyl-1,2,4-triazol bis(4-cyclohexyl thiosemicarbazone) ligand, H(5)L(1), is described. Treatment of H(5)L(1) with K(2)PtCl(4) gave the dinuclear complex Pt(H(3)L(1)), 1, but using MCl(2)(PPh(3))(2) where M = Pd or Pt, mononuclear complexes 2 and 3, of general formula [M(H(3)L(1))PPh(3)], were obtained. Subsequent reaction of the [Pd(H(3)L(1))PPh(3)] complex with PdCl(2)(PPh(3))(2) yielded a new dinuclear complex [(PPh(3))Pd(H(2)L(1))PdCl], 4. All compounds have been characterized by elemental analysis and FAB(+) spectrometry and by IR and NMR spectroscopy. The molecular structures of mononuclear complexes 2 and 3 and dinuclear complex 4 have been determined by X-ray crystallography. The new compounds synthesized have been evaluated for antiproliferative activity in vitro against NCI-H460, HepG2, MCF-7, A2780 and A2780cisR human cancer cell lines. The cytotoxicity data suggest that the H(5)L(1) ligand and Pt(H(3)L(1)), complex 1, may be endowed with important cytotoxic properties since they are capable of not only circumventing cisplatin resistance in A2780cisR but also exhibit antiproliferative activity in NCI-H460. The interactions of these compounds with calf thymus DNA were investigated by UV-vis absorption and a nephrotoxic study, in LLC-PK1 cells, has also been carried out.