The hypernetted-chain (HNC) equations solved on a three-dimensional cubic grid are employed to calculate the spatial distribution of the depletion potential between a big solute of arbitrary geometry and a big sphere immersed in small spheres forming the solvent. Effects of the step edge on the lateral depletion force along a wall surface are analyzed and shown to be in qualitatively good agreement with a recent experimental observation. Simple model Calculations are performed for the lock and key steric interactions between macromolecules, and it is found that the depletion effects provide the interactions with remarkably high selectivity. (C) 2002 Elsevier Science B.V. All rights reserved.