Samples of Lexan and Makrofol-E polycarbonate plastic track detectors were exposed to 1·1 MeV/N₅₄¹³²Xe-ions to investigate the thermal track fading properties of these plastics. The experimental results show that there is no effect of annealing on the bulk etch rate while the track etch rate decreases with annealing. The track diameter decreases with increase in annealing time and temperature. It is also observed that the track density is reduced as a result of annealing. The experiments reveal that the track lengths are, in general, decreased by the application of heat and that the oblique tracks are less stable than the vertical tracks. The decrease in diameter of₅₄¹³²Xe-ion tracks in Makrofol-E due to heat treatment is faster than that of₅₄¹³²Xe-ion tracks in Lexan.