The parameters predicted for the core of ITER plasmas are sufficiently different to those of existing tokamaks that a re-evaluation of the physics basis of ECE measurements is required. This is particularly important in the light of the detailed, and demanding, targets for the measurement of these parameters which have been set in the ITER design. In this paper we examine quantitatively the localisation of ECE Te measurements in the core and edge plasma, as well as the problem of access to the plasma centre at high Te. It is concluded that while ECE will be able to provide good measurements of Te for a wide variety of plasma conditions, the limitations need to be analysed in detail. We also look briefly into the possible potential of ECA as a divertor plasma diagnostic.