  We investigate the phase space structure of the relativistic Sitnikov problem
in the first post-Newtonian approximation. The phase space portraits show a
strong dependence on the gravitational radius which describes the strength of
the relativistic pericentre advance. Bifurcations appearing at increasing the
gravitational radius are presented. Transient chaotic behavior related to
escapes from the primaries are also studied. Finally, the numerically
determined chaotic saddle is investigated in the context of hyperbolic and
non-hyperbolic dynamics as a function of the gravitational radius.
