  We investigate different types of neutrino hot dark matter with respect to
structure formation and anisotropies in the cosmic microwave background
radiation (CMBR). The possibility of neutrino hot dark matter produced through
the decay of a heavier neutrino by the process nu_H -> nu_L + phi, where phi is
a scalar particle, is discussed in detail. This type of dark matter can
possibly be distinguished observationally from the standard neutrino dark
matter by using new CMBR data from the upcoming satellite missions MAP and
PLANCK.
