The dynamic fracture toughness of a reactor pressure vessel steel was investigated using small specimens. Precracked Charpy-size SE(B) specimens and circumferentially cracked round bars (CRB) loaded in tension were used to investigate the dynamic fracture toughness of an A533, Gr. B steel plate within the ductile-brittle transition region. The specimens used in this investigation were removed from the broken halves of conventional 4T C(T) specimens that had been utilized in a previous investigation of the dynamic fracture toughness of this material. Crack-tip loading rates in excess of 104 MPa-m1/2/s were achieved in the current tests. Multiple specimens were tested at each temperature in order to permit the determination of the reference temperature, T0. A fracture toughness scaling model for the circumferentially cracked round bar developed by Sciabetta was used to account for the loss of constraint in this specimen. A master curve approach was used to characterize the dynamic toughness in the ductile-brittle region. The shift in transition temperature was compared to a model for the strain rate dependence of T0 developed by Wallin. The shift in transition temperature of the CRB specimen was accurately predicted by the model. The CRB specimen and the dynamic SE(B) specimens gave good results considering the material inhomogeneity typical of the plate tested.