A comparsion was made of the sintering behaviour of 12Ce-PSZ powders prepared by coprecipitation and by mechanical alloying. Despite the presence of large aggregates, samples prepared from the chemically produced powders reached a high density after 3 h sintering at 1450 degrees C. The samples obtained by mechanical alloying of powders had the highest green density. However, owing to their wide agglomerate distribution and low-temperature agglomeration rate, they do not reach high density even after prolonged soaking at 1450 degrees C. The mechanically alloyed powders were flo-deflocculated to remove agglomerates as well as the electrostatic charge formed during their preparation. This treatment improved pressureless sinterability in air, and final densities close to the theoretical value were obtained.