A semi-analytical hard sphere reference system theory for calculation of solvent-mediated potential (SMP) is formulated for asymmetrical binary hard sphere mixture based on a recently proposed universal framework by the first two Letters of the series. Accuracy of the present semi-analytical theory for SMP and solid-liquid transition is affirmed. A theoretical way is devised to apply the reference system theory to SMP for case of general potentials, here a Lennard-Jones solvent bath, and the agreement between theory and available simulation data is satisfactory. (C) 2004 Elsevier B.V. All rights reserved.