Identification of heat-treated flint using ultra-violet light. Examination of flaked flints under ultra-violet light reveals differences in fluorescence caused by heating the flint prior to retouching it. This effect is especially marked on pre-dynastic Egyptian knives. On some examples, including the most beautiful in the Louvre, there seems to be several sequences of polishing, retouch and possible heat-treatment. Another example is a Solutrean laurel leaf from Laugerie Haute (Dordogne). On the other hand, flint from Grand-Pressigny does not show such differences in fluorescence after heating. This paper presents only preliminary results, and it remains to test other varieties of flint and wave lengths other than 2540 and 3660 A. The main intention here is to draw attention to this phenomenon, while awaiting further evidence and, it is hoped, a physical explanation