Aggressive liquids are often stored and transported in plastic vessel, tanks or tubes in chemical industry. Such plastic material is exposed to both mechanical and chemical stress. This stress causes penetration of liquids into plastics. Penetration of some liquids was studied by means of autoradiography. A special device was developed for the study of penetration of aggressive liquids into plastics under stress. This device and results of measurements of such penetration are described. It is shown that penetration occurs through microsplits in the studied system.