  It has been known that there are two schemes in the framework of three flavor
neutrinos to accommodate the global features of the hot dark matter neutrinos,
the solar neutrino deficit and the atmospheric neutrino anomaly in a manner
consistent with terrestrial neutrino experiments, i.e., hierarchical mass
neutrinos and almost degenerate neutrinos. We demonstrate that the recent
result by the CHOOZ experiment excludes the scheme of hierarchical neutrinos.
We also point out in the scheme of almost degenerate neutrinos that if
neutrinos are Majorana particles then the double $\beta$ decay experiments must
see positive signals on their way to reach a limit more stringent than the
present one by a factor of 5.
