Using 5-fluorouracil (5-FU) and cis-diamminedichloroplatinum(II) (cisplatin, CDDP) as starting compounds, 5-FU–cisplatin adducts cis-[Pt(NH ) (HFU)Cl] (1) and cis-[Pt(NH ) (HFU) ] (2) were prepared. The obtained complexes were characterized by IR, ES-MS and 32 32 2 1 H NMR spectroscopy. Complex 1 reacted with guanosine-59-monophosphate (59-GMP) and gave rise to a stable mixed-ligand complex cis-[Pt(NH ) (HFU)(GMP)] (3), whereas 2 did not undergo a similar reaction. In vitro cell growth inhibition tests of complexes 1 and 2 3 2 exhibited moderate antitumor activities against the melanoma B16-BL6 cell line. This work provides the basis for a potential alternative for the combinational use of 5-FU and CDDP in cancer therapy.  2002 Elsevier Science Inc. All rights reserved.