The large-strain tensile deformation of high-density polyethylene and high-density polyethylene filled with two volume fractions (f) of calcium carbonate particles is studied via an optical method. Digital image correlation is used to determine the local displacement gradients and full-field displacements during uniaxial tension tests on specimens of rectangular cross-section. A novel technique measures simultaneously, with a single camera, the deformation in all three dimensions. Full-field strain contours, macroscopic true stress-true strain behavior, and local volumetric strains are reduced from the raw test data. The true stress-true strain data shows an increase in modulus, but a decrease in yield stress and subsequent strain hardening, with increasing f. These results are strong evidence of particle debonding and are corroborated by an increase in volumetric strain with increasing f. (c) 2005 Elsevier Ltd. All rights reserved.