  Influence of quantum effects on the internal waves and the Rayleigh-Taylor
instability in plasma is investigated. It is shown that quantum pressure always
stabilizes the RT instability. The problem is solved both in the limit of
short-wavelength perturbations and exactly for density profiles with layers of
exponential stratification. In the case of stable stratification, quantum
pressure modifies the dispersion relation of the inertial waves. Because of the
quantum effects, the internal waves may propagate in the transverse direction,
which was impossible in the classical case. A specific form of pure quantum
internal waves is obtained, which do not require any external gravitational
field.
