The sintering behaviour of a number of commercially produced 8 mol% yttria-stabilized zirconia powders has been studied. The effect of different sintering regimes on the density and microstructure of the sintered ceramic was determined using density measurements, scanning electron microscopy (SEM) and dilatometry. The chemical homogeneity, particle size and the morphology of the as-received powder were related to the sintering behaviour of the different commercial powders. Powders prepared via a route which involved a spray-drying step sintered more readily than those prepared without a spray-drying step. Plasma-derived powders did not sinter to as high an apparent density as co-precipitated powders. The effect of sample density on the ionic conductivity of sintered YSZ ceramics was studied using a.c. impedance spectroscopy. This technique allowed separation of the bulk and grain-boundary components, enabling clear intepretation of the effects of sample porosity of the conduction pathways. Ceramics prepared from the three different powders achieved a bulk ionic conductivity of similar to 16 S cm(-1) at 1000 degrees C for sintered densities of 95% or greater. The results obtained are compared to values reported for a variety of other commercial powders. (C) 1998 Kluwer Academic Publishers.