For cubic ZrO2 single crystals deformed in  direction, new experimental data are presented on the flow stress and its strain rate sensitivity as well as on the dislocation densities and the distances between glide obstacles along the dislocations. A model is proposed to describe the strong variation of the parameters of the plastic deformation below 1000 K. It assumes that the mechanisms controlling the dislocation motion change from the pinning by localized obstacles above a transition temperature, e.g. small precipitates or jogs, to the overcoming of the Peierls relief at lower temperatures. The model is in agreement with most of the experimental observations. (C) 1998 Acta Metallurgica Inc.