Cavitation behaviour during high-temperature tensile testing in fine-grained 3 and 8 mol% yttria-stabilized zirconia has been compared. The 8 mol% yttria-stabilized zireonia (8Y-CSZ) had a single cubic phase, while the 3 mol% yttria-stabilized zirconia (3Y-TZP) was predominantly tetragonal. Internal cavities developed in both materials during superplastic deformation. The results demonstrated that the extent of cavitation in 8Y-CSZ was much higher than in 3Y-TZP under the same test conditions. In 8Y-CSZ, most of the cavities propagated in a direction perpendicular to the tensile axis as in most ceramics (with increasing strain these grew and interlinked to form cracks leading to failure at relatively low strains), whereas, in 3Y-TZP cavities were elongated parallel to the tensile axis as in metals. This difference arose from severe grain growth in 8Y-CSZ. (C) 2002 ELsevier Science B.V All rights reserved.