  In the seesaw model with hierarchical Dirac masses, the neutrino mixing angle
exhibits the behavior of a narrow resonance. In general, the angle is strongly
suppressed, but it can be maximal for special parameter values. We delineate
the small regions in which this happens, for the two flavor problem. On the
other hand, the physical neutrino masses are hierarchical, in general, except
in a large part of the region in which the mixing angle is sizable, where they
are nearly degenerate. Our general analysis is also applicable to the RGE of
neutrino mass matrix, where we find analytic solutions for the running of
physical parameters, in addition to a complex RGE invariant relating them. It
is also shown that, if one mixing angle is small, the three neutrino problem
reduces to two, two flavor problems.
