The fracture toughness of a number of different line-pipe materials is being determined through the use of experiments in which fractures are purposely started in full-size pressurized pipe specimens. The toughness is expressed in terms of fracture speed, surface appearance, and fracture pattern in the pipe specimens. These characteristics, obtained from experiments at different temperatures, are being correlated with laboratory fracture tests in order that a criterion for minimum acceptable fracture toughness may be defined. This report summarizes the results to date.