A recently developed marker-based technique for mapping of the displacement gradient tensor and the strain throughout the bulk of optically opaque specimens is presented and applied to an aluminium alloy multicrystal. Through investigations at 4%, 10% and 14% axial strains, the internal strain field is observed to be non-homogenous with the observed patterns present throughout the range of strains investigated. The morphology of the strain field is visualized with a resolution better than 50 mu m and variations are tentatively associated with the grain structure as recorded by EBSD. Future applications of the technique in combination with other 3-dimensional approaches are discussed with respect to comparison with Finite Element modelling approaches. (c) 2007 Elsevier Inc. All rights reserved.