Significant advances have recently been made in the numerical characterization of particle boundaries. However, progress in the numerical characterization of particle surfaces is slow. There are two fundamental issues associated with this problem: i.e., the acquisition of reliable three-dimensional (3-D) surface data and numerical description of the 3-D surface features. In this paper, the first issue is addressed while the second issue will be addressed in our next papers. Pairs of field emission scanning electron microscope (FESEM) stereo images of wear particles found in synovial joints have been acquired. A specially developed stereoscopy method was applied to the acquired FESEM images in order to obtain 3-D surface topography data of wear particles. The surface topography data obtained from the wear particles was then processed to produce: the range image, the contour map and the shaded image of a particle surface. The surface topography of wear particles was also shown in the colour stereo images. The results obtained in this study have clearly demonstrated that 3-D surface topography data of wear particles is very helpful in particle visualization and it can be used in numerical description of the surface. (C) 1999 Elsevier Science S.A. All rights reserved.