The fuel stringer in the United Kingdom commercial advanced gas-cooled reactor (AGR) is threaded onto a nimonic PE16 tie bar. During the loading and unloading of fuel, the tie bar supports the full weight of the fuel stringer. Therefore, studies have been undertaken to determine the effect of reactor exposure on the mechanical properties of PE16. Part of this program has included scanning Auger microscopy (SAM). This paper describes the application of this technique to the study of irradiated PE16 tie bar material. The first part of the SAM PE16 program was performed on various casts of unirradiated material with the objective of confirming that the alloy PE16 could be fractured in an intergranular manner in the scanning Auger microprobe and to develop techniques for handling active specimens. The paper describes the procedures adopted to overcome the problems of fracturing a radioactive nimonic PE16 alloy in an intergranular manner and reports results that have been obtained on active specimens from three tie bars. It is demonstrated that irradiation causes enrichment of nickel and depletion of chromium and iron at the grain boundaries together with segregation of the minority elements phosphorus and silicon. In addition, the annealing of irradiated material at 600°C for 1 h causes the grain boundary composition to return towards the as-manufactured state but does not fully reverse the effects of radiation.