  The neutrinoless double beta decay as well as any other laboratory experiment
has not been able to answer the question of the neutrino's nature. Hints on the
answer are available when neutrino oscillations and $(\beta\beta)_{0 \nu}$ are
considered simultaneously. In this case phenomenologically interesting neutrino
mass schemes can lead to non-vanishing and large values of $<m_{\nu}>$. As a
consequence, some schemes with Majorana neutrinos can be ruled out even now. If
we assume that in addition neutrinos contribute to Hot Dark Matter then the
window for Majorana neutrinos is even more restricted, e.g. GENIUS experiment
will be sensitive to scenarios with three Majorana neutrinos.
