  The MSW or vacuum oscillation solution of the solar neutrino problem can be
reconciled with possible existence of the $(\beta\beta)_{0\nu}$ decay with a
half-life corresponding to an effective Majorana mass of the electron neutrino
$|m_{ee}| \cong (0.1 - 1.0)~$eV. The phenomenological consequences of such a
possibility are analyzed and the implications for the mechanisms of neutrino
mass generation are considered.
