Specimens containing surface cracks were tested in either tension or bending to compare the stress intensity factor at failure with plane strain fracture toughness (KIc) in an International Cooperative Test Program. The material was heat treated to σys = 1 587 MPa and KIc = 54 MPan1/2. Because substantial stable crack growth occurred for some specimens, the test plan was modified to include detecting the onset of crack growth. It is shown that Pmax and the original fatigue precrack size cannot be employed to calculate Kmax for comparison with KIc when significant stable crack growth occurs. However, using Pinit (load at which stable crack growth is initiated) and the original fatigue precrack size to calculate Kmax or Kϕ=30° provides a very useful comparison with KIc. The influence of variations in fatigue precrack configuration on test results are also discussed.