An important contribution to the force between colloidal particles, which is missing in the DLVO theory, is the effect of volume exclusion among the solvent molecules. If the colloidal particles and solvent molecules are approximated as large and small hard spheres, this volume exclusion force can be calculated from the radial distribution function for a pair of large spheres. Using the Percus-Yevick approximation, an explicit expression for this force, valid for all separations, is botained. In addition, earlier results for the Percus-Yevick hard-sphere radial distribution function and hard-spher/hard-wall interfacial density profile are extended to arbitary distances. © 1988.