The synthesis and chemical characterization of two trans platinum complexes, (1) trans-[PtCl(2)NH(3)(2-hydroxymethylpyridine)] and (2) trans-[PtCl(2)NH(3)(3-hydroxymethylpyridine)], are described. The structures and chemical behaviour of these compounds have been compared to those of their isomer (3) trans-[PtCl(2)NH(3)(4-hydroxymethylpyridine)] previously studied. X-ray structures of all of them were solved and some interesting differences were found. The values of the dihedral angle (85 degrees , 57 degrees and 42 degrees for 1, 2 and 3, respectively) demonstrate how important is the position of substituent from a structural point of view. Studies of circular dichroism (CD), electrophoretic mobility (EM) in agarose gel and atomic force microscopy (AFM) showed differences in the modifications caused by the three complexes on DNA. Studies of antiproliferative activity of complexes 1 and 2 against cell tumour lines (HL-60) and apoptosis assays have also been carried out, showing that 1 as well as 2 are far less active than the previously described complex 3 (IC(50)=19; 19 and 3 microM, respectively). This fact probes that slight modifications on the drug's design may generate significant differences in the final antitumour activity by modifying the DNA-drug adducts, performance of resistance mechanisms and all the factors that play a fundamental role in Pt complexes' cytotoxicity.