Experimental, analytical, and archaeological evidence is presented to describe the characteristics of thermal alteration in mesolithic assemblages from the northern Netherlands. Experiments, both in the field and in the laboratory, have established the sequence of changes that occur when flint is subjected to heat. Analytical techniques involving the scanning electron microscope and thermoluminescence analysis are used in an attempt to recognize thermal pretreatment and to define the stages in manufacturing in which it was used. The proportions and spatial distributions of thermally-altered artefacts are employed to compare archaeological assemblages and to locate heat sources on occupation floors. In spite of high incidence of heat alteration in the assemblages, there is no conclusive evidence for intentional thermal pretreatment.