The purpose of this investigation was to determine the chemical composition, confirmed on X-ray diffraction analysis, of some commercially available dental gutta-percha cones. In addition, their plasticity in response to temperature variations was studied by differential scanning calorimetry. Great chemical heterogeneity was found among gutta-percha cones of different origin as well as within the same brand between small and large sizes. Barium sulfate determined radiopacity, zinc oxide influenced the inherent plasticity, while an excess of gutta-percha seemed to produce brittle gutta-percha cones which were unusable in clinical practice. Differential scanning calorimetry measured accurately the thermal ranges within which gutta-percha cones show a maximal plasticity without any chemical damage. It was also possible to define the thermal optimums for heat carriers, which could lead to more appropriate use of these instruments in endodontic therapy, whatever method may be used.