Laser ranging measurement of the lunar orbit (LLR) is examined for its ability to detect any spatial anisotropy in the gravitational interaction. Considering this possibility within the framework of energy - momentum-conserving generalizations of post-Newtonian metric gravity, it is found that the amplitude of an Earth - Moon range oscillation of frequency ( twice sidereal-anomalistic) is the system's most sensitive probe of any effective anistropy in gravity. Given the very significant improvement in precision of LLR data which has been achieved over the last decade, anisotropy of Newton's coupling parameter G at five parts in should be detectable with LLR. This is equivalent to measurement of the preferred frame PPN coefficient to two parts in .