Success of endodontic therapy depends upon both operator's skill and quality of the employed instruments. K-files have been examined for they probably are the most commonly used endodontic instruments. It is particularly important to take into consideration, together with the original quality of the instruments, its possible changes due to the wear from sterilization. In this paper have been therefore evaluated the characteristics of brand-new K-files from three different manufacturers together with the wear of the same instruments after paraformaldehyde steam sterilization.