The hardness of aluminum films on silicon are measured as functions of depth of the indenter. The films have thicknesses of 0.25, 0.5, and 1.0μm. The adhesion between one film and the substrate has been reduced through the prior deposition of a 10 nm layer of carbon. In each case the hardness is found to increase as the indenter approaches the film-substrate interface, but the rate of increase is greater for a film with good adhesion than for one with poor adhesion. It is suggested that this increase results from the constraint on deformation of the film by the substrate. A physical model is proposed whereby the yield stress of the film, σ0, and an average effective shear strength τ of the indenter-film and film-substrate interfaces, may be determined from the data. © 1988, Center for the Study of Law and Religion at Emory University. All rights reserved.