The glow-peak 5a of LiF:Mg,Ti is a glow-peak, with peak maximum temperature between those of glow-peaks 5 and 6. This glow-peak is not seen in the usual glow-curve, resulting after normal annealing at 400°C for 1 h and at 100°C for 2 h. However, its existence is confirmed first experimentally and then as the necessity to achieve a very good glow-curve fitting. In the present work it is found that the glow-peak 5a can be very well isolated from its neighbouring glow-peaks, after special thermal treatment between 140°C and 160°C. The isolation permits the study of its individual behaviour, which was found to have the following peculiarities. (i) This glow-peak is clearly seen only after thermal treatment between 140°C and 160°C. (ii) It appears with the same properties after both pre-irradiation and post-irradiation annealing in the above temperature region. (iii) Its activation energy was found to be above 3 eV and its frequency factor above 10 30 s −1 . These values are extremely high and outside the physically accepted limits.