Cisplatin, cis-[Pt(Cl 2 (NH 3 ) 2 ], can crosslink residues His67 of domain I and His247 of domain II in human albumin, occupying the major binding site for the essential metal zinc on the protein.Cisplatin is a widely used anticancer agent, particularly effective for treating solid tumors such as ovarian, testicular, bladder, head and neck cancers. 1 In vivo, cisplatin is converted to its active forms by aquation, 2 being highly reactive toward biomolecules such as DNA 3 and proteins. 4 Although DNA is probably the crucial target for cisplatin inducing apoptosis and cell death, 5 it is now increasingly recognized that an understanding of its reactions with proteins is very important for understanding its metabolism and side-effects. One day after intravenous administration, 65 to 98% of cisplatin is bound to blood plasma proteins, 6 and most of the Pt (50-61%) from cisplatin added to human blood plasma at physiologically-relevant doses is bound to albumin. 7 Albumin, a 66 kDa single-chain protein consisting of 3 isostructural domains, 8 and present in blood at ca. 0.6 mM, can bind and transport a variety of endogenic and exogenic substances, such as fatty acids, bilirubin, pharmaceuticals and metal ions. 9 Despite numerous reports on the interaction of cisplatin with albumin, few Pt binding sites have been characterized unambiguously. According to NMR spectroscopic studies, 10 a Met298 S,N-macrochelate is a major cisplatin binding site, and monofunctional adducts involving Cys34 and surface histidine residues are also be formed. Recently, Cys34, Met329, Tyr150 (or Tyr148) and Asp375 (or Glu376) were identified as cisplatin binding sites using multidimensional liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), after