The migration of lithium cations into the lattice of dioctahedral clays upon heating, considered up to now as irreversible, has been investigated. The samples under examination are two lithium-saturated montmorillonites, selected with different charge-deficit distributions between the tetrahedral and octahedral sheets, to obtain direct information on the structural changes occurring in both layers. Reexpansion of these samples previously collapsed at 300 degrees C has been attained, for the first time, under high vapor water pressures. A structural characterization of the smectites under the different treatments has been monitored by means of X-ray diffraction, XRD, Fourier transform infrared spectroscopy, FTIR, and Si-29, Al-27, and Li-7 magic angle spinning nuclear magnetic resonance, MAS-NMR. The effect that Li+ ions exert on the quadrupolar coupling constant of tetrahedral Al ions has been shown. Direct experimental evidence on the location of lithium ions in the hexagonal holes of the collapsed structure is provided. Additionally, generation of protons during the rehydration process is concluded.