Fracture toughness was determined for two nickel-chromium-molybdenum steels with linear-elastic and elastic-plastic methods. From the evaluation of linear-elastic/ideal plastic load-displacement curves and from the experimental results it follows that the relation of Merkle and Corten should be applied for J-integral determination for compact specimens. The extrapolation method for the determination of a critical J-value implies some problems. As an alternative it is proposed to determine J at a fixed distance from the blunting line. A comparison between stress intensity factors calculated from J and with linear-elastic methods shows that linear-elastic fracture mechanics can be applied to much smaller specimens than given by the ASTM Test for Bane-Strain Fracture Toughness of Metallic Materials (E 399-74). The equivalent-energy method and measurement of crack tip opening displacement with different clip gages at different distances from the crack tip yield stress intensity factors in agreement with the J-integral method.