a process for ascertaining the adhesive behaviour of pressure - sensitive adhesive flat materials such as medicinal adhesive tape and , in particular , pressure - sensitive adhesive application systems such as transdermal therapeutic systems is characterized in that a flat material with an adhesive layer of a defined coating weight per unit area and of defined quality of the adhesive mass is adhered with predetermined surface pressure and at a predetermined temperature to an elastic carrier film of defined thickness and elasticity , and that said carrier film is clamped into a test cell , in the manner of a membrane , between half - shells of a test cell , and that the carrier film along with the adhered flat material is subjected , in chronologically repeated sequence , to loading and unloading with alternating elastic stretchings by defined loading forces from the side facing away from the flat material , and that a detachment of the adhesive layer , which detachment arises progressively per unit of time , is observed and qualitatively and / or quantitatively evaluated .