The effects of high energy electron radiation on poly(ether ether ketone) (PEEK) have been investigated by differential scanning calorimetry (d.s.c.), transmission electron microscopy (TEM) and solvent extraction. It has been shown by extraction that irradiation results in the formation of crosslinks which affect the crystallization and reorganization kinetics and disrupt crystal structures. The d.s.c. behaviour is described in terms of two regimes : up to similar to 66 MGy the observed effects principally result from changes in the amorphous regions, whereas at higher doses crystal destruction appears to become increasingly important such that by 260 MGy only a small residual melting peak is observed. This characteristic radiation response can be employed as an expedient to prevent molecular reorganization without extensively disrupting the lamellar population. In this way the d.s.c. behaviour of PEEK has been studied in the absence of complications caused by annealing. It is shown that although some reorganization does normally occur, the high temperature melting endotherm is not purely an artifact of the experimental procedure. TEM examination reveals well-defined lamellar morphologies, even in specimens that have been irradiated to such a level that little or no d.s.c. endotherm remains. Despite the absence of a distinct d.s.c. melting transition, the morphology of such samples changes dramatically on heating to above their nominal melting temperature.