The changes in sensitivity of a cellulose triacetate (CTA) film dosimeter is reported as a function of linear energy transfer (LET). The change in molecular weight of poly(methyl methacrylate) (PMMA) is also reported. For both materials, little or no LET effect was observed up to a threshold LET, but the sensitivity or radiation yield decreased with increasing LET above this threshold level. The threshold LET level was similar for both polymers, occurring at around a few hundreds of MeV cm(2) g(-1), with this level probably corresponding to the overlapping of spurs along the ion’s path.