Various shaded hidden-surface display techniques have been used to render voxel data. In this paper, an approach to using general ray tracing for the rendering of voxel data is presented. Central to this approach is the interpolation of a surface with respect to the volume of a given voxel and its neighbors. Nine columns (of three voxel volumes each) provide sufficient constraints on the integral of a biquadratic function over the column's base to solve its specific coefficients. The use of these locally interpolated surfaces to define a scene to be ray traced is investigated.