The powder morphology and particle size of both mixtures of ultrafine yttria-doped zirconia (3 to 8 mol % Y2O3) and aluminium hydroxide (0 to 20 wt % Al2O3), and zirconia/yttria/alumina coprecipitated powders were studied using measurements of surface area, X-ray diffraction, differential thermal analysis, infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. All the powders were calcined at 800 degrees C for 10 minutes. Both the growth of zirconia crystallites and its crystallization temperature were strongly influenced by the presence of alumina. The crystallite zirconia growth was inhibited and the zirconia crystallization temperature was increased. This behaviour has been assumed to be due to the formation of a polycondensed chain of the type Zr-O-Al-O-Y-O-Al-O-Zr in which the diffusion distances were considerably augmented.