Few crack-arrest data are available for irradiated reactor pressure vessel steels, in part because the specimens commonly used to investigate crack-arrest behavior are relatively large (200 mm square by 50 mm thick). This paper addresses the question of specimen-size requirements for crack-arrest testing of irradiated RPV steels and offers several recommendations with regard to specimen size, specimen design, and testing procedures for efficient utilization of the limited space available in irradiation capsules.