It has been argued that since a power-law mantle may appear to the postlogical rebound process as linear if the rebound stress is less than the ambient tectonic stress, therefore, observations of rebound cannot be used to determine whether the flow law in the mantle is linear or nonlinear. The purpose of this paper is to show that this may not be completely true if the rebound process sees the steady-state creep. It will be demonstrated that for sites near the center of rebound, the relative sea level (RSL) observations cannot distinguish a Newtonian mantle from a Power-law mantle with large ambient stress. However, for sites outside the ice margin, the RSL signature for a power-law mantle is clearly distinguishable from that due to deep flow in a Newtonian mantle. This characteristic of a power-law medium is independent of the ambient stress level and is unlikely to change with more complicated rebound models. If these results remain valid in future work, then RSL data near the ice margin can be used to argue against a steady-state power-law mantle. ¿ American Geophysical Union 1995