[en] The possibility of using subsize specimens to monitor the properties of reactor pressure vessel steels is receiving increasing attention for light-water reactor plant life extension. This potential results from the possibility of cutting samples of small volume form the internal surface of the pressure vessel for determination of the actual properties of the operating pressure vessel. In addition, plant life extension will require supplemental data that cannot be provided by existing surveillance programs. Testing of subsize specimens manufactured from broken halves of previously tested surveillance Charpy specimens offers an attractive means of extending existing surveillance programs. Using subsize Charpy V-notch-type specimens requires the establishment of a specimen geometry that is adequate to obtain a ductile-to-brittle transition curve similar to that obtained from full-size specimens, and the development of correlations for transition temperature and upper-shelf energy (USE) level between subsize and full-size specimens. Five different geometries of subsize specimens were selected for testing and evaluation. The specimens were made from several types of pressure vessel steels with a wide range of yield strengths, transition temperatures, and USEs. The effects of specimen dimensions, including notch depth, angle, and radius, have been studied. The correlations of transition temperatures determined from different types of subsize specimens and the full-size specimens are presented. A new procedure for transforming data from subsize specimens is developed. The transformed data are in good agreement with data from full-size specimens for materials that have USE levels less than 200 J