As part of the DTI programme on the development of test methods for characterisation of advanced materials, project CAM 7 Electroactive materials properties under conditions of high stress or stress rate, has the overall aim of defining and improving the measuring framework for electroactive materials which will enable them to be used with greater confidence by UK industry. This report describes the results of experiments that have been developed to characterise piezoelectric ceramic materials at high electrical and mechanical stresses. The change in dielectric and piezoelectric properties with time at exposure to such stresses is reported in this document. Additionally, the experimental measurement methods - although described in a previous report (NPL Report CMMT (A) 116) - are re-visited and discussed in terms of the results which have been produced.