Dichloro(ethylenediamine)platinum(II), Pt(en)Cl(2), was dissolved in H(2)O and D(2)O, and the resulting aqueous solutions were electrosprayed into a quadrupole ion-trap mass spectrometer. A series of major and minor ionic hydrolysis products were detected. These ions were then subjected to collision-induced dissociation. As an aid in interpreting the experimental results, density functional theory calculations were carried out. These computations permitted the structures and energetics associated with the hydrolysis products to be determined. An understanding of the hydrolysis of PtenCl(2) and related coordination complexes is essential in the rational design of metal-based drugs.