This paper presents the results of a study on degradation due to irradiation occurring in WWER-440 reactor pressure vessel (RPV) steel, using subsize Charpy specimens (5×5×27.5 mm3). An application of subsize specimens for estimation of irradiation embrittlement of RPV steel has been substantiated. Comparison between ductile-to-brittle transition temperatures (DBTT) for full-size and subsize Charpy specimens has been carried out. The relation between these two values has been clarified. The results of testing trepans and templates cut out from WWER-440 reactor pressure vessels are considered. The main results of the program TACIS-91/1.1. are discussed.