  An approach aimed to extend the applicability range of non-relativistic
microscopic calculations of electronuclear response functions is reviewed. In
the quasielastic peak region the calculations agree with experiment at momentum
transfers up to about 0.4 GeV/c while at higher momentum transfers, in the
region about 0.4 - 1 GeV/c, a disagreement is seen. In view of this, to
calculate the response functions a reference frame was introduced where
dynamics relativistic corrections are small, and the results pertaining to it
were transformed exactly to the laboratory reference frame. This proved to
remove the major part of the disagreement with experiment. All leading order
relativistic corrections to the transition charge operator and to the one--body
part of the transition current operator were taken into account in the
calculations. Furthermore, a particular model to determine the kinematics
inputs of the non-relativistic calculations was suggested. This model provides
the correct relativistic relationship between the reaction final-state energy
and the momenta of the knocked-out nucleon and the residual system. The above
mentioned choice of a reference frame in conjunction with this model has led to
an even better agreement with experiment.
