  We have analyzed the results of the latest terrestrial neutrino oscillation
experiments in the framework of a model with mixing of three massive neutrinos
and a neutrino mass hierarchy ($ m_1 << m_2 << m_3 $). In this model,
oscillations of the terrestrial neutrinos are characterized by three
parameters, $ \Delta m^2 = m_3^2 - m_1^2 $ and the squared moduli of the two
mixing matrix elements $U_{e3}$ and $U_{\mu3}$. Using the results of
disappearance experiments and solar neutrino experiments, it is shown that only
two regions of possible values of $|U_{e3}|^2$ and $|U_{\mu3}|^2$ are allowed:
I. $|U_{e3}|^2$ and $|U_{\mu3}|^2$ are both small and II. $|U_{e3}|^2$ is small
and $|U_{\mu3}|^2$ is large. If the mixing parameters are in the region I, $
\nu_\mu <-> \nu_e $ oscillations are suppressed. In this case the LSND
indication in favor of $ \nu_\mu <-> \nu_e $ oscillations is not compatible
with the negative results of all other experiments. If the mixing parameters
are in the region II, $ \nu_e <-> \nu_\tau $ oscillations are strongly
suppressed. If massive neutrinos are Majorana particles, our analysis shows
that neutrinoless double-beta decay could be observed in the experiments of the
next generation only if the mixing parameters are in the region I.
