Electrospray ionization has been used to create the cupric ion hydrate [Cu(H2O)(4)](2+) Collisional. activation and dissociation of this ion in a triple sector electrostatic mass spectrometer leads to the formation of the doubly charged ions [Cu(H2O)(3)](2+), [Cu(H2O)](2+) and [Cu(H2O)](2+). The observation of the latter two ions vindicates the results of published theoretical calculations [El-Nahas et at., Chem. Phys. Lett. 318 (2000) 333], which predicted the stability of the cupric ion solvated by one or two water molecules and refutes the belief of Stace et al. [Chem. Phys. Lett. 329 (2000) 173] that their pick-up experiments prove that [Cu(H2O)(3)](2+) is the lowest stable gas-phase hydrate of the cupric ion.