  We use a statistical-mechanical identity closely related to the familiar
virial theorem, to derive unbiased estimators for spatial distribution
functions of classical fluids. In particular, we obtain estimators for both the
fluid density rho(r) in the vicinity of a fixed solute, and for the pair
correlation g(r) of a homogeneous classical fluid. We illustrate the utility of
our estimators with numerical examples, which reveal advantages over
traditional histogram-based methods of computing such distributions.
