The Materials Properties Council (MPC) conducted a cooperative testing program with the objective of developing a set of data to be used in the evaluation of the use of the precracked Charpy specimen (PCCV) for the determination of T?. This paper reports on the results of this program.A total of nine laboratories from four countries participated in the cooperative testing program.Each of the laboratories conducted experiments in accordance with the published version of ASTM Standard Test Method E1921-97 in order to obtain the T? values. T? was determined from data obtained at three test temperatures, -120°C, -100°C and -75°C. These temperatures were chosen to test the requirements of E1921. The -100°C temperature is the optimum test temperature for this size specimen, while -75°C is a marginal test temperature because there would be a number of tests which would be invalid. The -120°C temperature is below the optimum test temperature and may require a large number of tests to obtain T?, or result in an invalid data set.Over 250 fracture toughness tests were conducted on the specimens fabricated from the weld metal used in this program, with 60 or more tests at each test temperature. These results have been analyzed and the To temperature determined for each of the three primary test temperatures.The effect of number of specimens at the individual test temperatures has been determined.These results are compared with the T? results for larger size specimens also available for the test material.