J_Ic was determined in two materials (6061-T651 aluminum and ASTM A-723 Grade 1, Class 4 pressure vessel steel) using arc-tension (A(T)) and compact tension (C(T)) specimens. The J-R curves were determined by using the multispecimen method and the compliance unloading method. J was determined for the A(T) specimen by the Merkle-Corten method of analysis as modified by Clarke and Landes. A correction factor was included to account for the tensile loading component, and both the plastic and elastic components of J were necessary when using the A(T) specimen. With the proper formulas for J in the A(T) specimen, the same J-R curves were determined in both materials using either A(T) or C(T) specimens. This preliminary study suggested that the A(T) specimen was totally adequate for J_Ic testing and should be included in subsequent versions of ASTM Test for J_Ic, A Measure of Fracture Toughness (E 813).