The frequency-dependent dielectric constant of the Drude-Lorentz model of a nonpolar fluid is shown to have universal scaling behavior in the limit of low density. We derive an exact expression for the universal dielectric constant, and calculate it in a self-consistent ring approximation. The absorption line shape is found to be a shifted and asymmetrically distorted Lorentzian, as suggested by computer simulation data for systems of hard spheres and of atoms with Lennard-Jones interactions. A calculation of correction terms accounting for pair correlation effects leads to fairly good agreement with existing computer simulation data. (C) 1997 American Institute of Physics.