The fracture toughness of abrasion-resistant white cast irons has been measured, using precracked compact specimens. Some procedures used for precracking the brittle cast irons were outside the ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-72) requirements but still gave valid results. The excellent reproducibility, combined with a range in toughness values of 17.5 to 28.5 ksi√in. (19.2 to 31.4 MN/m^3/2) for abrasion-resistant white cast irons, provided the sensitivity necessary to distinguish differences in the toughness of white cast irons resulting from variations in composition or microstructure. The fracture toughness of three commonly used irons, 27Cr, 9Cr-6Ni, and 20Cr-2Mo-1Cu, was compared in the as-cast (and stress-relieved) condition. Heat treating the 20Cr-2Mo-1Cu iron substantially increased the hardness and reduced the fracture toughness slightly.