  The rotational and deformation properties of superdeformed fission isomers in
the $A\sim 240$ mass region have been investigated within the framework of the
cranked relativistic Hartree-Bogoliubov theory. The dependence of the results
of the calculations on the parametrization of the RMF Lagrangian has been
studied. The rotational properties are best described by the NL1 force.
