High-pressure Raman scattering measurements for the structure I of methane hydrate (MH) and methane deuterohydrate (MDH) have been performed at 296 K in order to observe the vibration of guest methane molecule in the host water cage. An analysis of the peak frequencies of the lattice vibrations of MH and MDH shows that the guest vibration in the large cage appears at similar to 50 cm(-1), being based on the clear distinction between the guest and host vibrations by deuteration of the host cage. (c) 2007 Elsevier B.V. All rights reserved.