  In this paper we deal with Radon transforms for generalized flag manifolds in
the framework of quasi-equivariant D-modules. We shall follow the method
employed by Baston-Eastwood and analyze the Radon transform using the
Bernstein-Gelfand-Gelfand resolution and the Borel-Weil-Bott theorem. We shall
determine the transform completely on the level of the Grothendieck groups.
Moreover, we point out a vanishing criterion and give a sufficient condition in
order that a D-module associated to an equivariant locally free O-module is
transformed into an object of the same type. The case of maximal parabolic
subgroups of classical simple groups is studied in detail.
