Copper oxide dopants in amounts up to 1 wt% were added to 2.5 mol% yttria-coated zirconia powders in studies of sintering, microstructure, mechanical properties and hydrothermal ageing behaviour. High densities (> 6 Mgm(-3)), high tetragonal phase content (> 95%), and phenomenal fracture toughness values (> 17 MPam(1/2)), were obtained for lower dopant levels. Grain sizes of 0.13 to 0.25 mu m were measured for all samples sintered at 1300 degrees C. Rounded pores in some doped samples indicated that a liquid phase was involved during sintering. Copper oxide additions aid low temperature sintering and offer potential for property enhancement with a particularly high toughness being measured as well as improving resistance to structural degradation in 180 degrees C hydrothermal ageing.