The dry sliding wear behavior of 3 mol% tetragonal zirconia polycrystals (3Y-TZP) and a composite containing 20 vol.% SiC whiskers have been examined by transmission electron microscopy. High wear rates for the TZP were associated with dramatic microstructural changes. The extreme outer ∼ 400 nm consisted of an amorphous surface layer containing both alumina and zirconia. Below this, the t-ZrO₂ grain size was an order of magnitude smaller than in the starting material. At a depth of 1–2 μm the tetragonal grains had become elongated, with a maximum aspect ratio of 30 : 1. The first monoclinic zirconia was found at a depth of 5 μm. In contrast, the composite exhibited a wear rate 5 orders of magnitude lower, associated with minor microstructural changes.