  The question of general covariance in quantum gravity is considered in the
first post-Newtonian approximation. Transformation properties of observable
quantities under deformations of a reference frame, induced by variations of
the gauge conditions fixing general invariance, are determined. It is found
that the one-loop contributions violate the principle of general covariance, in
the sense that the quantities which are classically invariant under such
deformations take generally different values in different reference frames. The
relative value of this violation is of the order 1/N, where N is the number of
particles in a gravitating body.
