Lagrangians forn point masses at the second post-Newtonian approximation of general relativity

We study the effect of an infinitesimal coordinate transformation on the Lagrangian and on the metric functional of a system ofn point masses. We show how to compute the Lagrangians ofn point masses at the second postNewtonian approximation of general relativity in different coordinate systems. The Lagrangians are shown to depend on the accelerations except in a special class of coordinates. This class includes the coordinates associated with the canonical formalism of Arnowitt, Deser, and Misner, but excludes most other coordinate systems used in the literature (notably the harmonic one).