Measurements on the creep strain attributable to grain boundary sliding, ∈gb, have frequently been performed on the specimen surface. However, thus far there has been no investigation using correct techniques to show that such surface measurements are also representative of the specimen interior. Measurements of egb using methods which are correct in principle for both surface and interior grain boundaries have been made for a number of copper/aluminum alloys and for type 316 stainless steel. It is shown that for these materials under the test conditions employed egb, is in fact the same for both surface and interior. It is also shown that it is possible to obtain βgb simply and easily from a single parameter such as the mean height of surface steps, •v, provided the required constant •k, relating •v and βgb is determined by correct methods for the material being considered.