Measurements of the plane strain fracture toughness KIc of sintered steels have frequently been invalid because the requirement that Pmax/PQ<1.1 (where Pmax = maximum load and PQ=load used to calculate KIc) has not been met. We show that the reason for the criterion not being met is that sintered steels have a considerable crack growth resistance KR. Values obtained in the past for KIc probably have been over-estimates of the initiation value of the crack growth resistance Ki and under-estimates of the maximum crack growth resistance K∞. The important point is that the assessment of the toughness of sintered steels by a single parameter is not appropriate. Test methods to determine the crack growth resistance of sintered steels are discussed. Crack growth, which is difficult to detect by visual observation, can be determined by compliance techniques. Because of the porous nature of sintered steel, fatigue cracks are unnecessary at the tip of the notch and indeed are undesirable as they can easily cause errors in toughness measurements through inadvertent overloading. The thickness requirement for plane strain measurements can also be relaxed.