Describes a method for determining environmental stress cracking (ESC) resistance of sheets and of flat test specimens, especially the sensitivity of their localized surface regions, of plastics from a constant prestrain test which will be indicated by change of a suitably chosen indicative property of specimens that have been prestrained for a definite time in the environment. Suitable for determining ESC caused by gases and liquids as well as by solids containing migrating substances in contact with a specific polymer. Illustrates test specimen P with defined strain in the outer surface, example of sandwiched test specimen and graphical evaluation of test results. AMD 9463 RENUMBERS THIS STANDARD